Flex board columns

What does this MR do?

Making issues board columns flexable

Notes:

• Duplicate of !8754 (closed) by @Rosulk 🎉 🎉

Why was this MR needed?

More user friendly view.

Screenshots (if relevant)

Original Behavior

• Lists have a fixed width
• Lists are easily clipped in a fairly large display 🙁

Proposed Behavior (with Flex)

Large Display:

Medium Display:

Small Display:

• Lists have a flexible width with fixed min / max 🙂

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [ ] Documentation created/updated
• [ ] API support added
• [ ] Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • [ ] Has been reviewed by a Backend maintainer
  • [ ] Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?