Keep existing parameters when redirecting metrics dashboard

What does this MR do?

Currently, when the metrics dashboard is opened, if the URL does not have the environment parameter, we redirect the user to the metrics dashboard of the default environment. Unfortunately, while redirecting, we remove all parameters and add the environment parameter. This results in the page redirecting to the default dashboard even if the user has selected another dashboard.

This MR changes the redirect behavior to add the environment parameter while retaining any existing parameters.

I've not added a changelog since the MR introducing the redirect was merged a few days back: !40608 (merged).

Issue: #243495 (closed)

Screenshots

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