Enable external status checks mutation for Projects::AllBranchesRule

Related to Support status checks for all branches (#478016 - closed)

What does this MR do and why?

Enable external status checks mutation for Projects::AllBranchesRule

We accidentally disabled the graphql mutations for BranchRules ExternalStatusChecks for Projects::AllBranchesRule records. This is incorrect, we do allow external status checks to be configured for All branches.

This change updates the service classes to allow external status checks for all branches. It also updates the mutation specs to ensure this is possible through the GraphQL API.

Changelog: fixed EE: true

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

1. Find a project in your GDK, note the full path e.g. gitlab-org/gitlab
2. In the console find the project Project.find_by_full_path('gitlab-org/gitlab')
3. Note the ID from the project, it should be displayed in the console, or you can call project.id
4. Open Graphql Explorer
5. Create an external status check, the last value in the branchRuleId for Projects::AllBranchesRule is the project ID, replace the value you noted in step 3.

mutation TestMutation($branchRuleId: ProjectsBranchRuleID!, $name: String!, $externalUrl: String!) {
  branchRuleExternalStatusCheckCreate(input: {
    branchRuleId: $branchRuleId
    name: $name
    externalUrl: $externalUrl
  }) {
    externalStatusCheck {
      id
      name
      externalUrl
    }
    errors
  }
}

variables

{
  "branchRuleId": "gid://gitlab/Projects::AllBranchesRule/41",
  "name": "ping",
  "externalUrl": "https://gitlab.com"
}

6. Edit the status check (if you don't have the ID from the last step you can paste this into the console and replace the last value in the id variable below MergeRequests::ExternalsStatusCheck.last.id

mutation TestMutation($id: MergeRequestsExternalStatusCheckID!, $branchRuleId: ProjectsBranchRuleID!, $name: String!, $externalUrl: String!) {
  branchRuleExternalStatusCheckUpdate(input: {
    id: $id
    branchRuleId: $branchRuleId
    name: $name
    externalUrl: $externalUrl
  }) {
    externalStatusCheck {
      id
      name
      externalUrl
    }
    errors
  }
}

variables

{
  "id": "gid://gitlab/MergeRequests::ExternalStatusCheck/14",
  "branchRuleId": "gid://gitlab/Projects::AllBranchesRule/41",
  "name": "pong",
  "externalUrl": "https://gitlab.com"
}

7. Delete the rule

mutation TestMutation($id: MergeRequestsExternalStatusCheckID!, $branchRuleId: ProjectsBranchRuleID!) {
  branchRuleExternalStatusCheckDestroy(input: {
    id: $id
    branchRuleId: $branchRuleId
  }) {
    errors
  }
}

variables

{
  "id": "gid://gitlab/MergeRequests::ExternalStatusCheck/14",
  "branchRuleId": "gid://gitlab/Projects::AllBranchesRule/41"
}