[Frontend] Add group/subgroup option in policy scope

Why are we doing this work

1. Policy scope will now have fourth option: scoping to a group
2. This issue adds new option to policy_scope dropdown

Relevant links

Non-functional requirements

• Documentation:
• Feature flag: policy_group_scope
• Performance:
• Testing: unit tests

Implementation plan

1. Add new option in ee/security_orchestration/components/policy_editor/scope/scope_section.vue
2. Add dropdown for with/without exceptions
3. Make sure yaml is updated accordingly
4. Make sure UI reflects changes in yaml

Verification steps