Add weight input component to swimlanes board sidebar

What does this MR do?

Related to #37105 (closed). This feature is behind the :boards_with_swimlanes feature flag.

This adds the weight input to the swimlanes board sidebar. It doesn't fetch any data as the weight is provided by the stored issue.

Screenshots

Setting and removing weight

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