man: always prefix links to uapi specs with their UAPI.XY spec number

Let's try to establish the spec numbers, by mentioning them in most doc
links.

Follow-up for: https://github.com/uapi-group/specifications/pull/187

man/bootctl.xml

@@ -81,7 +81,7 @@
 
     <para>These commands are available for all boot loaders that
     implement the <ulink
-    url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot
+    url="https://uapi-group.org/specifications/specs/boot_loader_specification">UAPI.1 Boot
     Loader Specification</ulink>, such as
     <command>systemd-boot</command>.</para>
 
@@ -90,7 +90,7 @@
         <term><option>list</option></term>
 
         <listitem><para>Shows all available boot loader entries implementing the <ulink
-        url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot Loader Specification</ulink>, as well as any
+        url="https://uapi-group.org/specifications/specs/boot_loader_specification">UAPI.1 Boot Loader Specification</ulink>, as well as any
         other entries discovered or automatically generated by a boot loader implementing the <ulink
         url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>.
         JSON output may be requested with <option>--json=</option>.</para>
@@ -126,7 +126,7 @@
     <title>Boot Loader Interface Commands</title>
 
     <para>These commands are available for all boot loaders that implement the <ulink
-    url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot Loader Specification</ulink> and the <ulink
+    url="https://uapi-group.org/specifications/specs/boot_loader_specification">UAPI.1 Boot Loader Specification</ulink> and the <ulink
     url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>, such as
     <command>systemd-boot</command>.</para>
 
@@ -152,7 +152,7 @@
         boot loader entry. These special IDs are resolved to the current values of the EFI variables
         <varname>LoaderEntryDefault</varname>, <varname>LoaderEntrySysFail</varname>, <varname>LoaderEntryOneShot</varname>
         and <varname>LoaderEntrySelected</varname>, see <ulink url="https://uapi-group.org/specifications/specs/boot_loader_specification">
-        Boot Loader Specification</ulink> for details.
+        UAPI.1 Boot Loader Specification</ulink> for details.
         These special IDs are primarily useful as a quick way to persistently make the currently booted boot loader
         entry the default choice, or to upgrade the default boot loader entry for the next boot to the default boot
         loader entry for all future boots, but may be used for other operations too.</para>
@@ -314,7 +314,7 @@
         are applied to file system in the indicated disk image. This option is similar to
         <option>--root=</option>, but operates on file systems stored in disk images or block devices. The
         disk image should either contain just a file system or a set of file systems within a GPT partition
-        table, following the <ulink url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable Partitions
+        table, following the <ulink url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">UAPI.2 Discoverable Partitions
         Specification</ulink>. For further information on supported disk images, see
         <citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
         switch of the same name.</para>
@@ -444,7 +444,7 @@
       <varlistentry>
         <term><option>--make-entry-directory=yes|no</option></term>
         <listitem><para>Controls creation and deletion of the <ulink
-        url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot Loader Specification</ulink> Type #1 entry
+        url="https://uapi-group.org/specifications/specs/boot_loader_specification">UAPI.1 Boot Loader Specification</ulink> Type #1 entry
         directory on the file system containing resources such as kernel and initrd images during
         <option>install</option> and <option>remove</option>, respectively. The directory is named after the
         entry token, as specified with <option>--entry-token=</option> parameter described below, and is
@@ -705,7 +705,7 @@ Boot Loader Entries:
     <title>See Also</title>
     <para><simplelist type="inline">
       <member><citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
-      <member><ulink url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot Loader Specification</ulink></member>
+      <member><ulink url="https://uapi-group.org/specifications/specs/boot_loader_specification">UAPI.1 Boot Loader Specification</ulink></member>
       <member><ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink></member>
       <member><citerefentry><refentrytitle>systemd-boot-random-seed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
     </simplelist></para>