Replica lag monitor

[levkk]

Description

Monitor replica lag. #215

[codecov]

Codecov Report

❌ Patch coverage is 57.47508% with 128 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pgdog/src/admin/show_replication.rs	0.00%	55 Missing ⚠️
pgdog/src/backend/pool/lsn_monitor.rs	42.37%	34 Missing ⚠️
pgdog/src/backend/pool/shard/monitor.rs	62.50%	15 Missing ⚠️
.../src/backend/replication/logical/publisher/slot.rs	0.00%	9 Missing ⚠️
pgdog/src/backend/pool/shard/mod.rs	85.00%	6 Missing ⚠️
pgdog/src/admin/parser.rs	0.00%	3 Missing ⚠️
pgdog-config/src/database.rs	0.00%	2 Missing ⚠️
pgdog/src/backend/pool/inner.rs	66.66%	1 Missing ⚠️
...nd/replication/logical/publisher/publisher_impl.rs	0.00%	1 Missing ⚠️
pgdog/src/frontend/client/test/mod.rs	0.00%	1 Missing ⚠️
... and 1 more

📢 Thoughts on this report? Let us know!