Add feature tests for merge request approval policy

What does this MR do and why?

Add feature tests for merge request approval policy on project level

This MR covers all invalid polices and tests backend validation

EE: true

MR acceptance checklist

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Screenshots or screen recordings

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*** NO VISUAL CHANGES***

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

bundle exec rspec ee/spec/features/projects/security/user_creates_merge_request_approval_policy_spec.rb

Related to #486692