Continue improvements for time window filtering on metrics dashboard

What does this MR do?

Time window filtering in the monitoring dashboard is currently a dropdown with a pre-defined list of time windows. In this MR, a form is added thus enabling the user to enter custom time windows.

Known issues:

1. Time window dropdown doesn't resize very well on smaller screen sizes. This is okay for MVC as discussed here #29513 (comment 220356928)
2. The time window dropdown control is unable to retain the previously selected value. This is an existing issue and has to be handled in a separate MR #33158 (closed) SOLVED
3. The time window dropdown does not close with the cancel button programmatically. This is also a known issue. I'm working on a MR against gitlab-ui (gitlab-ui!815 (merged)). SOLVED
4. Time window control, when is at its longest cannot be clicked near the caret. This is because it is hiding under a flex container. SOLVED

Screenshots

Scenarios	Screenshot
Placeholder, valid datetime format
Invalid state, valid date format
Valid state
Invalid start/end in URL params

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance 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

Closes #29513 (closed)