chore(Dashboard): Ensure shared label colors are updated

[geido]

SUMMARY

Follow-up PR for #30646 to ensure that when certain dimensions or metrics are removed or no longer present in the charts, the stored shared_label_colors can detect these changes and reflect the current state. This is achieved by comparing all labels across all charts to infer the shared ones once a Dashboard has rendered all its charts.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N.A.

TESTING INSTRUCTIONS

1. Enter an existing Dashboard
2. Update a chart that has shared labels with other charts
3. Remove those dimensions/metrics from the chart
4. Ensure that when going back to the dashboard the dashboard is being updated with current shared label colors (by checking the network activity)

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[michael-s-molina]

Isn't this a fix instead of a chore?

[fisjac]

Looks good to me