udev/v4l_id: convert to VERB_COMMAND and add --introspect-cli

The custom help() is replaced by a COMMAND() description, and
--introspect-cli is added. The abstract is changed to the imperative.
There is no man page for this udev helper, so none is referenced.

test/units/TEST-74-AUX-UTILS.introspect-cli.sh

@@ -109,6 +109,7 @@ INTROSPECTABLE=(
     timedatectl
     updatectl
     userdbctl
+    v4l_id
     varlinkctl
 )