[Frontend]: Add KEV filter to a policy editor

Why are we doing this work

See parent epic for more detilas

Relevant links

1. Design

Non-functional requirements

• Documentation:
• Feature flag: security_policies_kev_filter
• Performance:
• Testing: Unit tests

Implementation plan

1. Add new filter component to ee/app/assets/javascripts/security_orchestration/components/policy_editor/scan_result/rule/scan_filters
2. Connect new component to ee/app/assets/javascripts/security_orchestration/components/policy_editor/scan_result/rule/security_scan_rule_builder.vue
3. Make sure it is behind feature flag
4. Add tests

Verification steps