Don't add duplicate entries to pg_auth

If we create 2 database entries for pgbouncer, with the same user account, then two entries get added to pg_auth. We should parse this ahead of time and only create one entry.

/cc @jtevnan

marked this issue as related to #2571

assigned to @ibaum

changed milestone to %10.0

added HA Pick into Stable postgresql labels

created branch 2721-don-t-add-duplicate-entries-to-pg_auth

mentioned in merge request !1945 (merged)

closed via merge request !1945 (merged)

mentioned in commit 4f5c7fff

mentioned in commit 1218734c

mentioned in commit 17d1e04b