Add support for SAST in security policies

What does this MR do and why?

This change adds new scan type to Security Orchestration Policies: SAST. This MR also adds new way to execute scans in enforced pipeline: in child pipeline.

Screenshots or screen recordings

How to set up and validate locally

1. Create new project (you can import ie. https://github.com/digininja/DVWA)
2. Go to Security Policy -> Policies, click on New Policy, select Scan Execution as Policy type.
3. Paste policy:

   type: scan_execution_policy
   name: 'SAST test'
   description: 'SAST test'
   enabled: true
   rules:
     - type: pipeline
       branches:
         - master
   actions:
     - scan: sast

4. Create new MR with updated policy and hit merge.
5. In your project add .gitlab-ci.yml file and add simple config:

   image: busybox:latest
   
   test:
     stage: test
     script:
       - echo "Do a test here"

6. Go to your project -> CI/CD -> Pipelines and click Run Pipeline

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 #340722 (closed)