Refactor selecting active board item from Vuex to Apollo

What does this MR do and why?

Refactors setting active board item from VueX to Apollo.

This is part of Apollo boards migration &9026 (closed)

Behind :apollo_boards feature flag.

This impacts Group Issue Board ,Project Issue Boards and Epic Boards.

Note: There is an existing issue causing an error in console when closing the sidebar or switching selected item. It has been raised separately as it is not related to this change: Boards - Console error when closing sidebar (#403574 - closed)

Screenshots or screen recordings

How to set up and validate locally

1. Turn on :apollo_boards feature flag
2. Open a board
3. Select a card and verify that the information displays properly in the sidebar
4. Editing works, including updating cards, expect for title as mentioned on the code.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #381038 (closed)