Add labels component to swimlanes board sidebar

What does this MR do?

Related to #37104 (closed). This feature is behind the :boards_with_swimlanes feature flag.

This adds the label select to the swimlanes board sidebar. The select component (labels-select) uses the REST API to internally fetch/search labels, and this wrapper updates the selected labels using GraphQL.

Screenshots

Label selector behavior

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