Align pgmonitor with Containers

[benjaminjb]

Description

Containers alerts/dashboards have some changes; this PR aligns the two sources:

• fixing some queries that are now compatible with the OTel and postgres-exporter options
• adding some alerts requested by users

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

• Bugfix
• Enhancement
• Breaking Change
• Documentation

Testing

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

Code testing

Have you tested your changes against:

• RedHat/CentOS
• Ubuntu
• Not applicable

If your code touches sql_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

[hunleyd]

@benjaminjb not critical but would be nice if you setup commit verification (either via SSH key or GPG key) so we don't have:

Commits must have verified signatures.