Generalize filter selector

What does this MR do and why?

Generalize filter selector

• prepare for Create CI variable filter for scan execution po... (!122979 - merged) (and make that MR smaller)
• make component reusable for multiple policy types
• move filter variable to a prop
• move selected into a prop
• update tests

Changelog: changed

EE: true

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Page	Before	After
Scan result policy - default		No visual change
Scan result policy - scan - none selected		No visual change
Scan result policy - scan - all selected		No visual change
Scan result policy - license		No visual change

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Upload a GitLab Ultimate license
2. Navigate to a project/group => Secure => Policies => New policy => Scan result policy
3. Verify a user can add filters
4. Save the policy with variables
5. Navigate to a project/group => Secure => Policies => Edit policy
6. Verify the editor populates the filters

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 #412790 (closed)