Refactor fetching epic lanes from VueX to Apollo

What does this MR do and why?

Refactor board swimlanes, fetching epics lanes from VueX to Apollo.

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

Behind :apollo_boards feature flag.

This does not include fetching issues in unaassigned lane, only epic and issue within those epics.

This impacts Group and Project Issue Boards.

Screenshots or screen recordings

How to set up and validate locally

1. With :apollo_boards feature flag, load an issue board.
2. Click Group by and select epic in the top right dropdown.
3. Verify that epics and there issue load properly.

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 #381031 (closed)