Add manuals-upstream-translation-update to api-site

The api-site repository, prior to being moved out of
openstack-manuals used to publish its content to tx for
translation. This patch re-starts that behaviour, by adding
the translation-update job to the api-site repo's config
in zuul. Similarly, the periodic propose-translation-update
task was omitted.

The manuals-upstream-translation-update is the correct job
for this repo, since it contains XML files and will post
translatable resources to the openstack-manuals group on tx.

Change-Id: I1d713ab004162ef73c906ecbd288ca60611eb3b6
Fix CLI args for welcome-message

The welcome-message script uses SSH arguments that are the same
as expire-old-reviews, not trivial-rebase. This patch updates
the hook script to use the correct CLI arguments.

Change-Id: Ib771e2a8cf4b770878dd24c72efd80344e62f754
Merge "Add manuals-upstream-translation-update to api-site"
Merge "Fix CLI args for welcome-message"