Update packages required for each CI job.
Update packages required for each CI job.

Documentation builds and tests have only a few packages in common so rearrange packages to save some time and clarify dependencies.

Remove the libperl-dev package which became obsolete when the LibC module was removed in 79cfd3ae.

Add a few comments for good measure.

pgmasters/backrest,pgmasters/backrest,pgbackrest/pgbackrest,pgbackrest/pgbackrest,pgbackrest/pgbackrest