Auto-generated iterations should not have dates in titles

Auto-generated iterations within a cadence have start/due dates in titles hardcoded.

We should make the necessary changes to avoid hardcoding dates because keeping titles/dates in sync would become progressively harder as the feature (and the data records) evolves. The initial motivation for the hardcoding of dates was to allow searching by dates along with titles.

Backend Tasks

• Remove the backend logic that inserts start/due dates into iteration titles when iterations are created in advance for a cadence (!72846 (merged)).

Frontend Tasks

• Update the frontend to utilize iteration dates (start/due) separately and display them
  • Update the iterations list (!72847 (merged)).
  • Update the iterations widget in the issue/board sidebar (!72847 (merged)).
  • Update the iterations dropdown in the board list create form and in the board list header (!72847 (merged)).
  • Update the iterations dropdown appearing in the filtered search bar (vue issues list) (!74044 (merged)).