Remove `value_stream_analytics_path_navigation` feature flag [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

This MR removes the value_stream_analytics_path_navigation feature flag, this feature flag has been default enabled and is deemed ready.

This MR:

• Removes references to the feature flag in the backend and frontend
• Removes all test blocks where we had the feature flag disabled
• Removes documentation for the feature flag

Note: There will be a follow-up MR to remove the old frontend navigation and stage table components that are no longer being used, but i left that out from here to keep this MR focused.

Screenshots (strongly suggested)

No visual changes as the feature has already been default enabled.

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 _____.
• 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

Related to #323982 (closed)