CLOS-2132: Detect postgresql.conf unix_socket_directories pre-upgrade and add explicit migration steps

[prilr]

Add a second report in postgresqlcheck that fires when postgresql-server is installed AND /var/lib/pgsql/data/postgresql.conf contains an active "unix_socket_directories" (plural) setting.

Root cause confirmed from 3 separate cases.

CL7's postgresql-server 9.2 ships with a forward-compatible patch that accepts the newer (PG 9.3+) plural parameter name
"unix_socket_directories" - so postgres runs fine on CL7 with that setting. RHEL-8's postgresql-upgrade package, which provides the old 9.2 server binary that pg_upgrade launches to read the data-old cluster, ships an unpatched 9.2 build that rejects the plural form with:

  LOG:  unrecognized configuration parameter "unix_socket_directories" in file "/var/lib/pgsql/data-old/postgresql.conf"
  FATAL: configuration file "/var/lib/pgsql/data-old/postgresql.conf" contains errors
  pg_ctl: could not start server

The default RHEL-7 postgresql.conf has the plural line commented out by default, but admin edits, cPanel tooling, and config-management commonly uncomment it (it's "the modern form" per current PG docs).

Users hit by this saw their migration fail with a confusing socket-connection error - the actual cause is buried in pg_upgrade_server.log.

The new check:

• Reads /var/lib/pgsql/data/postgresql.conf if it exists.
• Matches "^\sunix_socket_directories\s=" (active, not commented).
• Emits a HIGH-severity report with a concrete sed remediation (rename plural -> singular) for both pre-upgrade and post-upgrade cases.
• Treats missing/unreadable files as "not affected" - if the data dir was never initialized (no initdb), the bug can't trigger.

Tests cover: the new detection function across plural / commented / singular / whitespace / buried / missing-file cases;
both that the new report fires only when postgresql-server is present and that it does not when the package is absent.