feat(datastore,postgres): add logical replication support to Postgres WatchAPI

[mazdakb]

An opt-in implementation of the Watch API for the Postgres datastore that streams changes from the WAL via logical replication (pgoutput), instead of polling the transactions table. Enabled with --datastore-watch-logical-replication-enabled.

[codecov]

Codecov Report

❌ Patch coverage is 69.50617% with 494 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/datastore/postgres/lsn_ledger.go	60.54%	245 Missing and 81 partials ⚠️
internal/datastore/postgres/watch_cursor.go	76.53%	89 Missing and 34 partials ⚠️
internal/datastore/postgres/revisions.go	83.57%	10 Missing and 2 partials ⚠️
internal/datastore/postgres/pgoutput_row.go	84.06%	8 Missing and 3 partials ⚠️
internal/datastore/postgres/options.go	74.20%	8 Missing ⚠️
internal/datastore/postgres/postgres.go	85.72%	6 Missing ⚠️
...rations/zz_migration.0026_add_commit_lsn_ledger.go	54.55%	4 Missing and 1 partial ⚠️
internal/datastore/postgres/gc.go	78.58%	2 Missing and 1 partial ⚠️

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