Update PostgreSQL queries.

Cleanup pg_stat_user_tables:

• Update query and make more readable.
• Add database name column.
• Remove duplicate of COALESCE(last_vacuum, '1970-01-01Z').
• Drop n_mod_since_analyze.
• Collapse vacuum and autovacuum data.
• Collapse analyze and autoanalyze data.

gitlab-org/omnibus-gitlab#5654 (closed)

Signed-off-by: Ben Kochie bjk@gitlab.com