[grafana] Dashboards content validations improvements

[ghostinsoba]

Description

Additional validations is required:

• Check if datasource uid specified correctly
  (legacy, before Grafana 8.3: "datasource": "$datasource_uid", after "datasource": {"uid": "$datasource_uid"})

• Check if panel type is not deprecated
  (recommend to migrate from graph (old) to timeseries and from flant-statusmap-panel to state-timeline)

Changed existing flant-statusmap-panel deprecation recommendations from status-history to state-timeline

Why do we need it, and what problem does it solve?

Closes #8038

What is the expected result?

CI must fail for new pull requests that contain dashboards with deprecated forms of datasource UIDs and panel types

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: testing
type: chore
summary: Dashboard linter improvements.
impact_level: low