pg_upgrade: Optimize logical replication slot caught-up check.

pg_upgrade: Optimize logical replication slot caught-up check.

Commit 29d0a77fa6 improved pg_upgrade to allow migrating logical slots
provided that all logical slots have caught up (i.e., they have no
pending decodable WAL records). Previously, this verification was done
by checking each slot individually, which could be time-consuming if
there were many logical slots to migrate.

This commit optimizes the check to avoid reading the same WAL stream
multiple times. It performs the check only for the slot with the
minimum confirmed_flush_lsn and applies the result to all other slots
in the same database. This limits the check to at most one logical
slot per database.

During the check, we identify the last decodable WAL record's LSN to
report any slots with unconsumed records, consistent with the existing
error reporting behavior. Additionally, the maximum
confirmed_flush_lsn among all logical slots on the database is used as
an early scan cutoff; finding a decodable WAL record beyond this point
implies that no slot has caught up.

Performance testing demonstrated that the execution time remains
stable regardless of the number of slots in the database.

Note that we do not distinguish slots based on their output plugins. A
hypothetical plugin might use a replication origin filter that filters
out changes from a specific origin. In such cases, we might get a
false positive (erroneously considering a slot caught up). However,
this is safe from a data integrity standpoint, such scenarios are
rare, and the impact of a false positive is minimal.

This optimization is applied only when the old cluster is version 19
or later.

Bump catalog version.

Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: shveta malik <shveta.malik@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Discussion: https://postgr.es/m/CAD21AoBZ0LAcw1OHGEKdW7S5TRJaURdhEk3CLAW69_siqfqyAg@mail.gmail.com