[FE] Add admin setting to designate CSP group

Why are we doing this work

• users want to designate a CSP (Centralized Security Policies) group in the admin settings to apply instance-level policies

Relevant links

• see epic for design

Non-functional requirements

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

Implementation plan

• frontend add new section in settings at security_and_compliance.html.haml
• frontend create a new file in ee/app/views/admin/application_settings for the settings
• frontend create a group selector

Verification steps