Add BE validations specific to Gauge type panel YML

Problem to solve

At the moment, there are no YML validations for the gauge specific properties.

Given that the YML for a gauge type panel looks like this:

dashboard: 'Dashboard Title'
panel_groups:
  - group: 'Group Title'
    panels:
      - title: "Gauge"
        type: "gauge-chart"
        min_value: 0
        max_value: 100
        split: 20
        thresholds:
          mode: percentage # or absolute
          values: [65, 95]
        format: "kilobytes"
        metrics:
          - query: 'max(go_memstats_alloc_bytes{job="prometheus"})'
          - unit: kb

The client should receive warnings when:

• min_value or max_value have invalid values
• min_value > max_value
• split has invalid values (is negative, string, etc.)
• thresholds have invalid values (they don't have values between min_value and max_value, if percentage they don't have values between (0-100), etc.)
• format has invalid value

Intended users

User experience goal

Proposal

Further details

Permissions and Security

Documentation

Availability & Testing

What does success look like, and how can we measure that?

What is the type of buyer?

Is this a cross-stage feature?

Links / references