Update annotations graphql query

What does this MR do?

This MR updates the following on FE to match the GraphQL properties for annotations on BE

1. Annotations fetch GraphQL query params
   1. starting_at -> startingAt
   2. ending_at -> endingAt
   3. Added the dashboard start time so the annotation fetch is optimized
2. Annotations GraphQL response structure is updated
   1. Response structure and parsing logic
   2. Specs
   3. Mock data

Notes

1. Everything is still behind metrics_dashboard_annotations feature flag.
2. Happy to jump on a call to do a walkthrough demo if setting up the environment is an issue.

Screenshots

This is how the integration with backend looks like on the FE.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Mentions #211418 (closed)