Fix filling of missing position for closed lists

What does this MR do?

Assures that board relative position table is joined also when filling missing positions in closed lists. Join with this table was hooked to order_relative_position_on_board, but for closed lists this scope is not used.

This MR assures that .join_board_position is included if we either order epics by position or if we filter out epics which have position already set.

Related to #333370 (closed)

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

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