Expose tests total count in PipelineEntity

Part of #223134 (closed)

What does this MR do?

This MR exposes a new attribute in our PipelineEntity.

It includes the following items:

• Exposes tests_total_count attribute at the Pipeline level

This attribute would be used to display the number of total tests ran for a given pipeline as you can see below 👇

Why are we doing this?

Currently our badge counter is filled in by an async request to another endpoint that runs in parallel which needs to load and parse all reports taking approximately ~1min for gitlab.com. Since our JUnit counter data is now being stored in a database we can now expose it at the pipeline level and improve the ~performance of our JUnit feature.

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