Default on apollo_boards feature flag

What does this MR do and why?

Default on apollo_boards feature flag

Unstub FF in rspec tests

Screenshots or screen recordings

No visual changes. This migration does not change any board behaviour.

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 #381210 (closed)