Add iteration to issues created on scoped boards

What does this MR do?

For a board scoped to an iteration
Add that iteration to issues created on the board

Since boards don't yet support Cadences in boardConfig, we add a temporary extra query to get the cadence from the current iteration if the Current checkbox is selected on a board.

Testing:

1. Create an iteration that includes the current date
2. Load issue board, click Edit board and scope to Current iteration
3. Add a new issue to a list
4. Click the issue card, check that iteration was added to the issue

Screenshots

Screen_Recording_2021-10-13_at_5.38.24_pm

• Depends on !70007 (merged) for BE to support mutation
• Depends on !69052 (merged) to work with iteration_cadences feature flag enabled

Issue #300897 (closed)