Add milestone to new board new list form

What does this MR do?

Related issue: #241625 (closed)

Adds EE version of board_add_new_columne.vue.
Contains a List type select, and allows adding Milestone lists.

How to test

1. Enable :board_new_list feature flag 1, Load board
2. Click Create new list
3. Select 'Milestone list' from the dropdown

Screenshots (strongly suggested)

Label list (existing)	Milestone list

Related MRs

1. Groundwork MR !55460 (merged)
2. THIS MR - Add milestone list !55498 (merged)
3. Add iteration list !55500 (merged)
4. Add assignee list (WIP)

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • [-] I have included a changelog entry.
  • I have not included a changelog entry because this is behind a feature flag
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Separation of EE specific content