Define dashboard dropdowns layout in flex

What does this MR do?

Fix for #202541 (closed) and #211889 (closed)

Ensure the metric dashboard filter bar dropdowns and buttons are consistent in their width, and scale well on different screen sizes

• Removed column layout and used flex instead
• Fixed an issue with the dropdown tooltip
• Tested on mobile and tablet as well as desktop

Screenshots

before	after

Resize test

Tooltips

Small issue in tooltips has been fixed

Too many buttons? No problem!

When presented with many buttons, the layout adapts:

sm	md	lg

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