clusterdb: Allow specifying tables to process in all databases.

clusterdb: Allow specifying tables to process in all databases.

Presently, clusterdb's --table option cannot be used together with
--all, i.e., you cannot specify tables to process in all databases.
This commit removes this unnecessary restriction.  In passing,
change the synopsis in the documentation to use "[option...]"
instead of "[--verbose | -v]".  There are other general-purpose
options (e.g., --quiet and --echo), but the synopsis currently only
lists --verbose.

Reviewed-by: Kyotaro Horiguchi, Dean Rasheed
Discussion: https://postgr.es/m/20230628232402.GA1954626%40nathanxps13