chore: split branch protection policy for different spec types

[qduanmu]

Summary

This PR splits the branch protection rules.

Related Issues

• Closes CPLYTM-1374

Review Hints

With splited policies, complytime.yaml needs an update. e.g.,:

policies:
  - url: http://localhost:8765/policies/ampel-branch-protection
    id: ampel-bp
  - url: http://localhost:8765/policies/ampel-approval-requirements
    id: ampel-approvals
targets:
  - id: agcontent-branch-protection
    policies:
      - ampel-bp
    variables:
      url: https://gitlab.cee.redhat.com/group/project
      specs: builtin:gitlab/branch-protection.yaml
      branches: main
      access_token:  ${GITLAB_TOKEN}
      platform: gitlab
  - id: agcontent-approvals
    policies:
      - ampel-approvals
    variables:
      url: https://gitlab.cee.redhat.com/group/project
      specs: gitlab/project-approvals.yaml
      branches: main
      access_token: ${GITLAB_TOKEN}
      platform: gitlab

[qduanmu]

Per discussion, we prefer to avoid doing this split for less disruptive, there are similar scenarios in GitHub, and we need to find a common solution for this. For GitLab, there is an issue with BP-2.01 policy, which is using a different spec type, for now we prefer to mark it as a known issue.