Add dedicated security scan rule builder

What does this MR do and why?

This is Part 2 of 3 of breaking up the original MR !103744 (closed)

In this MR:

• Refactor the branch selection from the original security scan policy into policy_rule_branch_selection.vue‎
• Update policy_rule_builder_v2.vue‎ to show security scan policy if selected
• Add dedicated security_scan_r‎ule_builder.vue‎ - (note this is derived from the logic embedded in policy_rule_builder.vue, it will go away after we remove the feature flag.

Screenshots or screen recordings

Before & when flag off	After with flag on

How to set up and validate locally

• In a rails console enable Feature.enable(:license_scanning_policies)
• As a EE user Navigate to http://gdk.test:3000/<group>/<project>/-/security/policies
• Click New Policy button
• On the Scan Result Policy card click Select policy
• Add a security scan rule

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.

Related to #371506 (closed)