Add group level policy new page

What does this MR do and why?

• create initial backend helpers
• create update js pages to accommodate different types of namespaces

Related to #345317 (closed)

These changes are behind the :group_level_security_policies feature flag

These changes are not meant to result in a fully-functional page as this is behind a feature flag.

Screenshots or screen recordings

Page	Before	After
group/-/security/policies/new
project/-/security/policies/new		No change
project/-/security/policies/:policy/edit		No change

How to set up and validate locally

1. Enable :group_level_security_policies feature flag
2. Upload a GitLab Ultimate license
3. Navigate to a group => Security & Compliance => Policies
4. Navigate to a project => Security & Compliance => Policies

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.