Refactor coverage finder [RUN ALL RSPEC] [RUN AS-IF-FOSS]

Ref: #293825 (closed)

This is the last Step #4 to refactor our daily coverage data finder.

What does this MR do?

This MR removes our feature flag and make sure all codepaths are now using our new coverage finder.

It includes the following items:

• Move our new finder out of Ci::Testing namespace
• Remove DailyBuildGroupReportResultsByGroupFinder which is no longer used
• Remove feature flag

Why are we doing this?

As part of our effort to reduce our ~"technical debt", we are refactoring our daily coverage finder

This finder is used at 2 different places, so we decided to introduce a feature flag to mitigate the risk of ~performance degradation.

1. Aggregate daily coverage by project - https://gitlab.com/gitlab-org/gitlab/-/graphs/master/charts
2. Aggregate daily coverage by group - https://gitlab.com/groups/gitlab-org/-/analytics/repository_analytics

After making sure no ~performance degradation and no new ~bug where introduced since we enabled our feature flag flag this week.

We are now confident with the scalability of our code coverage feature.

Database review

No new SQL queries have been introduced by this MR.

Note: This finder has been reviewed by the database team in those 2 MRs.

• !53670 (merged)
• !54111 (merged)

In this MR we are merging our new finder with the old one at the right place by removin the Ci::Testing namespace.

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