[frontend] Allow repositioning epics on epic boards

What does this MR do?

Allows moving epics between lists on epic boards.

It also disables re-sorting epics on FE side - these epics are already sorted on BE side and sorting them by their relative position attribute is not correct (relative position is used in epic trees, but not on epic boards where position is stored per each board separately).

Related to #233441 (closed)

Frontend part of !59379 (merged)

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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