Organize security policy feature tests

Why are we doing this work

• the feature tests for security policies are hard to read and add to due to duplicate code and spread out tests
• we need to reorganize them so they can easily be added to

Relevant links

Non-functional requirements

• Documentation:
• Feature flag:
• Performance:
• Testing:

Implementation plan

• backend create more security policy shared examples
• backend move files from ee/spec/features/security/ to either ee/spec/features/projects/security and/or ee/spec/features/groups/security
• backend create more shared examples at spec/support/shared_examples/security/

Verification steps