Add policy rule builder for scan result policy

What does this MR do and why?

Add policy rule builder for scan result policy as an increment to the main body. It will be followed by a MR covering the policy action builder.

Follow up from !80101 (merged)
Related issue #351166 (closed)

Screenshots or screen recordings

Add, update and remove rules

How to set up and validate locally

1. Enable scan_result_policy feature flag
2. Create a security project as described in the docs
3. Create a new scan result policy with the project owner

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.