feat: drop support for PG9.6 and PG10. simplify common queries.

[keithf4]

Description

Drop support for PostgreSQL 9.6 and 10 per the support statement in docs (https://access.crunchydata.com/documentation/pgmonitor/latest/#postgesql)

Now that 9.6 is dropped, many queries that required being in version specific query files can be moved to the global query file. Re-organized common vs version specific queries in docs.

Bugfix: Included improved replica replay monitoring metric discussed in Issue #319

Please indicate what kind of change your PR includes (multiple selections are acceptable):

• Bugfix
• Enhancement
• Breaking Change
• Documentation

PRs should be against existing issues, so please list each issue using a separate 'closes' line:

closes #319

Testing

None of the testing listed below is optional.

• Installation method:
  • Binary install from source, version: 4.8
  • OS package repository, distro, and version: CentOS7
  • Local package server, version:
  • Custom-built package, version:
  • Other:
• PostgreSQL, Specify version(s): 15, 11
• docs tested with hugo version(s): 0.80.0

Code testing

Have you tested your changes against:

• RedHat/CentOS
• Ubuntu
• SLES
• Not applicable

If your code touches postgres_exporter, have you:

• Tested against all versions of PostgreSQL affected
• Ensure that exporter runs with no scrape errors
• Not applicable

If your code touches node_exporter, have you:

• Ensure that exporter runs with no scrape errors
• Not applicable

If your code touches Prometheus, have you:

• Ensured all configuration changes pass promtool check config
• Ensured all alert rule changes pass promtool check rules
• Prometheus runs without issue
• Alertmanager runs without issue
• Not applicable

If your code touches Grafana, have you:

• Ensured Grafana runs without issue
• Ensured relevant dashboards load without issue
• Not applicable

Checklist:

• I have made corresponding changes to:
  • the documentation
  • the release notes
  • the upgrade doc