Refactor daily coverage finder dates

Ref: #293825 (closed)

What does this MR do?

This MR moves our business logic to fetch daily coverage data by dates in our new finder.

We will now use default dates in case our params being sent by the frontend are nil:

• start_date will default the last 90 days.
• end_date will default the current date.

Why are we doing this?

As brought up by @ck3g:

Date.parse can raise an exception.

This MR aims to prevent it from happening in the future and also centralize all our business logic at the same place.

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