Allow refresh rate feature to be disabled via a feature flag

What does this MR do?

Allow refresh rate feature to be disabled

We should allow refresh rate feature to be disabled via feature flag.

Enabling refresh rate for all user might have impact in performance if too many of them enable it. We want to release this feature and monitor it's behavior.

Refs #229831 (closed)

Screenshots

disable_metric_dashboard_refresh_rate off	disable_metric_dashboard_refresh_rate on

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