Productivity Analytics: Refactor setPath action

What does this MR do?

This MR refactors the filter actions of the Productivity Analytics by setting the relevant filters on the state instead of setting a query string on the filters property.

The following changes were introduced:

• Remove filters from state and add authorUsername, milestoneTitle and labelName instead
• Rename setPath action
• introduce setFilters action instead which updates the newly added state properties instead of setting the path string

This is behind the productivity_analytics feature flag.

Screenshots

N/A

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

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