Boards new list for Assignee

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 Assignee lists.

How to test

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

Related MRs

1. Groundwork MR !55460 (merged)
2. Add milestone list !55498 (merged)
3. Add iteration list !55500 (merged)
4. Add assignee list THIS MR
5. UIify !55855 (merged)

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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

Availability and Testing