Refactor code coverage summary graphql resolver

Ref: #293825 (closed)

What does this MR do?

This MR refactors our CodeCoverageSummary resolver for our GraphQL API to use our new DailyBuildGroupReportResultsFinder.

Why are we doing this?

Now that we've extended our finder to be more flexible, we can start removing some duplicated code in our resolver to clean up more ~"technical debt".

This will allow us to centralize all our database business logic in our new finder.

Database review

Please note that we did not change our existing query introduced in !45831 (merged).

We just moved our business logic to our dedicated finder.

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • [-] I have included a changelog entry.
  • I have not included a changelog entry because we are refactoring some ~"technical debt".
• [-] 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