bootctl: automatically set --graceful when running in chroot

Installing stuff in a chroot should not fail because efivars are
not available. When running in a container touching efivars is
completely disabled, but there are some cases (recovery) where
it is needed to touch them in a chroot, so don't disable them but
avoid failing the run instead.

man/bootctl.xml

@@ -424,8 +424,9 @@
         <term><option>--graceful</option></term>
         <listitem><para>Ignore failure when the EFI System Partition cannot be found, when EFI variables
         cannot be written, or a different or newer boot loader is already installed. Currently only applies
-        to <command>is-installed</command>, <command>update</command>, and <command>random-seed</command>
-        verbs.</para>
+        to <command>is-installed</command>, <command>update</command>, <command>random-seed</command> and
+        <command>install</command> verbs. Since version v258, it is implicitly enabled when running inside a
+        chroot.</para>
 
         <xi:include href="version-info.xml" xpointer="v244"/></listitem>
       </varlistentry>