BE: Add approval_policies to GraphQL API and deprecate scan_result_policies

Why are we doing this work

We plan to move from "Scan result policy" to a new name "Merge request approval policy". Because of this, we should adapt backend to support both types.

In this issue, we should add approval_policies as a field to our GraphQL API and return the same results as for scan_result_policies.

We should also deprecate scan_result_policies.

Relevant links

• See epic
• Docs for GraphQL deprecations

Non-functional requirements

• Documentation: should be updated
• Feature flag:
• Performance:
• Testing:

Implementation plan

• Update NamespaceType and expose the data from scan result policies under approval_policies field
• Update ProjectType and expose the data from scan result policies under approval_policies field

Verification steps

1. Query for project's approvalPolicies and verify it returns the same data as for scanResultPolicies:

   query projectScanResultPolicies {
       namespace: project(fullPath: "gitlab-org/approval-policy-project") {
           id
           approvalPolicies(relationship: INHERITED) {
               nodes {
                   name
                   yaml
                   editPath
                   enabled
                   updatedAt
                   userApprovers {
                       id
                       name
                       webUrl
                   }
                   allGroupApprovers {
                       id
                       fullPath
                       webUrl
                   }
                   roleApprovers
               }
           }
       }
   }

2. Query for group's approvalPolicies and verify it returns the same data as for scanResultPolicies:

   query groupScanResultPolicies {
       namespace: group(fullPath: "gitlab-org/approval-policy-group") {
           id
           approvalPolicies(relationship: INHERITED) {
               nodes {
                   name
                   yaml
                   editPath
                   enabled
                   updatedAt
                   userApprovers {
                       id
                       name
                       webUrl
                   }
                   allGroupApprovers {
                       id
                       fullPath
                       webUrl
                   }
                   roleApprovers
               }
           }
       }
   }