man: systemd-stub places PCR public key in file 'tpm2-pcr-public-key.pem', stick to that name across the board

systemd-stub provides the signing key for TPM2 signed PCR policies in a
file tpm2-pcr-public-key.pem to userspace. Hence, to clarify that this
is the same key as used when signing via "systemd-measure", let's rename
it in the docs like that.

Also rename the private key to tpm2-pcr-private-key.pem, to keep the
symmetry.

With this we should universally stick to this nomenclature:

1. tpm2-pcr-public-key.pem   ← public part of signing key
2. tpm2-pcr-private-key.pem  ← private part of signing key
3. tpm2-pcr-signature.json   ← signature file made with key pair

Inspired by: #34069

man/systemd-measure.xml

@@ -286,9 +286,9 @@
       <title>Generate a private/public key pair, a unified kernel image, and a TPM PCR 11 signature for
       it, and embed the signature and the public key in the image</title>
 
-      <programlisting>$ openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out tpm2-pcr-private.pem
+      <programlisting>$ openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out tpm2-pcr-private-key.pem
 ..+.+++++++++......+.........+......+.......+....+.....+.+...+..........
-$ openssl rsa -pubout -in tpm2-pcr-private.pem -out tpm2-pcr-public.pem
+$ openssl rsa -pubout -in tpm2-pcr-private-key.pem -out tpm2-pcr-public-key.pem
 # systemd-measure sign \
      --linux=vmlinux \
      --osrel=os-release.txt \
@@ -296,25 +296,25 @@ $ openssl rsa -pubout -in tpm2-pcr-private.pem -out tpm2-pcr-public.pem
      --initrd=initrd.cpio \
      --splash=splash.bmp \
      --dtb=devicetree.dtb \
-     --pcrpkey=tpm2-pcr-public.pem \
+     --pcrpkey=tpm2-pcr-public-key.pem \
      --bank=sha1 \
      --bank=sha256 \
-     --private-key=tpm2-pcr-private.pem \
-     --public-key=tpm2-pcr-public.pem >tpm2-pcr-signature.json
+     --private-key=tpm2-pcr-private-key.pem \
+     --public-key=tpm2-pcr-public-key.pem >tpm2-pcr-signature.json
 # ukify --output=vmlinuz.efi \
      --os-release=@os-release.txt \
      --cmdline=@cmdline.txt \
      --splash=splash.bmp \
      --devicetree=devicetree.dtb \
-     --pcr-private-key=tpm2-pcr-private.pem \
-     --pcr-public-key=tpm2-pcr-public.pem \
+     --pcr-private-key=tpm2-pcr-private-key.pem \
+     --pcr-public-key=tpm2-pcr-public-key.pem \
      --pcr-banks=sha1,sha256 \
      vmlinux initrd.cpio</programlisting>
 
      <para>Later on, enroll the signed PCR policy on a LUKS volume:</para>
 
      <programlisting># systemd-cryptenroll --tpm2-device=auto \
-     --tpm2-public-key=tpm2-pcr-public.pem \
+     --tpm2-public-key=tpm2-pcr-public-key.pem \
      --tpm2-signature=tpm2-pcr-signature.json \
      /dev/sda5</programlisting>
 
@@ -339,38 +339,38 @@ $ openssl rsa -pubout -in tpm2-pcr-private.pem -out tpm2-pcr-public.pem
       two classes of secrets or credentials: one that can be unlocked during the entire runtime, and the
       other that can only be used in the initrd.</para>
 
-      <programlisting>$ openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out tpm2-pcr-private.pem
+      <programlisting>$ openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out tpm2-pcr-private-key.pem
 .+........+.+........+.......+...+...+........+....+......+..+..........
-$ openssl rsa -pubout -in tpm2-pcr-private.pem -out tpm2-pcr-public.pem
-$ openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out tpm2-pcr-initrd-private.pem
+$ openssl rsa -pubout -in tpm2-pcr-private-key.pem -out tpm2-pcr-public-key.pem
+$ openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out tpm2-pcr-private-key-initrd.pem
 ..+.......++........+........+......+........+....+.....+.+..+..........
-$ openssl rsa -pubout -in tpm2-pcr-initrd-private.pem -out tpm2-pcr-initrd-public.pem
+$ openssl rsa -pubout -in tpm2-pcr-private-key-initrd.pem -out tpm2-pcr-public-key-initrd.pem
 # ukify --output vmlinux-1.2.3.efi \
      --os-release=@os-release.txt \
      --cmdline=@cmdline.txt \
      --splash=splash.bmp \
      --devicetree=devicetree.dtb \
-     --pcr-private-key=tpm2-pcr-private.pem \
-     --pcr-public-key=tpm2-pcr-public.pem \
+     --pcr-private-key=tpm2-pcr-private-key.pem \
+     --pcr-public-key=tpm2-pcr-public-key.pem \
      --phases=enter-initrd,enter-initrd:leave-initrd,enter-initrd:leave-initrd:sysinit,enter-initrd:leave-initrd:sysinit:ready \
      --pcr-banks=sha1,sha256 \
-     --pcr-private-key=tpm2-pcr-initrd-private.pem \
-     --pcr-public-key=tpm2-pcr-initrd-public.pem \
+     --pcr-private-key=tpm2-pcr-private-key-initrd.pem \
+     --pcr-public-key=tpm2-pcr-public-key-initrd.pem \
      --phases=enter-initrd \
      vmlinux-1.2.3 initrd.cpio \
      --uname=1.2.3
 + /usr/lib/systemd/systemd-measure sign --linux=vmlinux-1.2.3 \
 --osrel=os-release.txt --cmdline=cmdline.txt --dtb=devicetree.dtb \
 --splash=splash.bmp --initrd=initrd.cpio --bank=sha1 --bank=sha256 \
---private-key=tpm2-pcr-private.pem --public-key=tpm2-pcr-public.pem \
+--private-key=tpm2-pcr-private-key.pem --public-key=tpm2-pcr-public-key.pem \
 --phase=enter-initrd --phase=enter-initrd:leave-initrd \
 --phase=enter-initrd:leave-initrd:sysinit \
 --phase=enter-initrd:leave-initrd:sysinit:ready
 + /usr/lib/systemd/systemd-measure sign --linux=vmlinux-1.2.3 \
 --osrel=os-release.txt --cmdline=cmdline.txt --dtb=devicetree.dtb \
 --splash=splash.bmp --initrd=initrd.cpio --bank=sha1 --bank=sha256 \
---private-key=tpm2-pcr-initrd-private.pem \
---public-key=tpm2-pcr-initrd-public.pem \
+--private-key=tpm2-pcr-private-key-initrd.pem \
+--public-key=tpm2-pcr-public-key-initrd.pem \
 --phase=enter-initrd
 Wrote unsigned vmlinux-1.2.3.efi
       </programlisting>
@@ -385,8 +385,8 @@ Wrote unsigned vmlinux-1.2.3.efi
       by the first <option>--pcr-private-key=</option> option, covering all boot phases. The
       <literal>.pcrpkey</literal> section is used in the default policies of
       <command>systemd-cryptenroll</command> and <command>systemd-creds</command>. To use the stricter policy
-      bound to <filename>tpm-pcr-initrd-public.pem</filename>, specify <option>--tpm2-public-key=</option> on
-      the command line of those tools.</para>
+      bound to <filename>tpm2-pcr-public-key-initrd.pem</filename>, specify
+      <option>--tpm2-public-key=</option> on the command line of those tools.</para>
     </example>
   </refsect1>