Enforce maximum SEP `action` count

Why are we doing this work

Once the application setting for the maximum SEP action count was introduced by #472213 (closed), we need to enforce the setting for both schedule and pipeline type SEP.

Relevant links

n/a

Non-functional requirements

• Documentation:
• Feature flag:
  • we need a feature flag that controls whether the application setting gets enforced for a project.
  • should use the same feature flag that #472213 (closed) uses to control the policy editor validation error message.
• Performance:
• Testing:

Implementation plan

• backend limit schedule type SEP actions (draft)
• backend limit pipeline type SEP actions (draft)

Verification steps

n/a