[Rails] Update Job API to return new native gitlab secrets manager format for secrets

We added support for native gitlab secrets manager to Runner in: #540909 (closed)

Now we need to update what Rails returns to runner for gitlab secrets manager secrets. Instead of masquerading as vault secrets, we will now return the following format:

{
  "secrets": {
    "DATABASE_PASSWORD": {
      "gitlab_secrets_manager": {
        "server": {
          "url": "https://openbao.gitlab.com",
          "inline_auth": {
            "auth_mount": "gitlab_rails_jwt",  // Just the mount name
            "jwt": "eyJ...",
            "role": "project_123_ci"
          }
        },
        "engine": {
          "name": "kv-v2",
          "path": "project_123/ci"
        },
        "path": "database_credentials",
        "field": "value"
      }
    }
  }
}

Related code: https://gitlab.com/gitlab-org/gitlab/-/blob/cdc3892b06837dfc718b6e355df64ec089cc01bf/ee/app/presenters/ee/ci/build_runner_presenter.rb#L12