feat(dashboard): expose the embedded dashboard configuration on the api

[agubler]

SUMMARY

Adds an embedded property to the existing dashboard API that returns the embedded configuration if it exists. This users can use the API with a single call to get a list of embeddable dashboards, whilst currently this would require an extra API request per dashboard.

TESTING INSTRUCTIONS

Run the branch, set the EMBEDDED_SUPERSET to True and configure a dashboard as embeddable within the UI. Request the dashboard api from /api/v1/dashboard and request the specific dashboard api from /api/v1/dashboard/{id} and review the embedded configuration.

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

If there are additional automated tests that need adding and/or if the embedded configuration on the API needs to be behind the same EMBEDDED_SUPERSET please let me know

[rusackas]

Thanks for the contribution, and sorry this slipped under the radar for so long. Would you be willing to give this a rebase? I'll add a couple potential reviewers in the meantime that might be able to assess/raise any api/scaling/security questions.