feat: support Postgres 17 in PostgreSQLDatabaseMetrics

[The-East-Wind]

This PR aims to resolve #6657

I'm creating this as a draft PR to confirm if the approach to fixing this is correct.

This has some rough edges which I'll be polishing once the approach is validated.

Stats removed in Pg 17 and their alternatives:

< Pg17	Pg17+
pg_stat_bgwriter.checkpoints_timed	pg_stat_checkpointer.num_timed
pg_stat_bgwriter.checkpoints_req	pg_stat_checkpointer.num_requested
pg_stat_bgwriter.buffers_backend	SUM(pg_stat_io.writes)
pg_stat_bgwriter.buffers_checkpoint	pg_stat_checkpointer.buffers_written

Reference: https://www.postgresql.org/docs/17/monitoring-stats.html

Rough edges:

1. Move the version check condition out of the consumer function to the registration level to avoid condition execution everytime consumer is invoked.
2. Implement a better pattern to have multiple stat sources (different views, tables, etc.) for the same metric and choosing one of them based on some condition (server version in this case).
3. Implemet a better pattern to easily map the metrics to their sources.
4. See if some form of parametrisation can be done to the integration tests to run the same tests against multiple postgres containers with different versions instead of creating duplicate integration test classes.

[shakuzen]

The general approach here looks good to me. I'm not sure if @jonatan-ivanov has any thoughts on it or not.