Fix backup status query

[benjaminjb]

Description

The backup status query was incorrectly changed before. This change uses the original query as a model, but simplifies the query based on the underlying metrics. This query was tested against both postgres_exporter and OTEL solutions in PGO.

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: PGO monitoring stack
• PostgreSQL, Specify version(s): 17
• docs tested with hugo version(s):

Code testing

Have you tested your changes against:

• RedHat/CentOS
• Ubuntu
• Not applicable

If your code touches Grafana, have you:

• [x ] 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