kernel-install: add header to generate entry files

I was looking at a bug in bugzilla about some boot loader issue, and it was
hard to say if the boot entry files were generated by our plugin or something
else. Add a header to make this clear.

kernel-install invokes the plugins via absolute path always, so $0 gives as
the full path the location where the plugin is installed. This is what we want:

  title      Fedora Linux 37 (Workstation Edition)
  # Boot Loader Specification type#1 entry
  # File created by /usr/lib/kernel/install.d/90-loaderentry.install (systemd 252-409-g5028904^)

src/kernel-install/90-loaderentry.install.in

@@ -138,6 +138,8 @@ mkdir -p "${LOADER_ENTRY%/*}" || {
 
 [ "$KERNEL_INSTALL_VERBOSE" -gt 0 ] && echo "Creating $LOADER_ENTRY"
 {
+    echo "# Boot Loader Specification type#1 entry"
+    echo "# File created by $0 (systemd {{GIT_VERSION}})"
     echo "title      $PRETTY_NAME"
     echo "version    $KERNEL_VERSION"
     if [ "$ENTRY_TOKEN" = "$MACHINE_ID" ]; then