Add GraphQL mutation to create a member role

What does this MR do and why?

It adds a mutation for creating a new custom role. We already have a REST API endpoint, but we agreed that we should aim for GraphQL endpoints in general. That's why I added this mutation after creating update mutation (!131358 (merged))

How to set up and validate locally

Run the following mutation in graphQL explorer (https://gdk.test:3443/-/graphql-explorer)

mutation {
  memberRoleCreate(input: {
    groupPath: "flightjs"
    name: "Role name", 
    description: "This is a new test role",
    readCode: true,
    readVulnerability: true,
    baseAccessLevel: GUEST
  }) {
    errors
    memberRole {
      id
      name
      description
      readVulnerability
      readCode
      enabledPermissions
      baseAccessLevel {
        integerValue
        stringValue
      }
    }
  }
}

Response

{ "data": { "memberRoleCreate": { "errors": [], "memberRole": { "id": "gid://gitlab/MemberRole/17", "name": "Role name", "description": "This is a new test role", "readVulnerability": true, "readCode": true, "enabledPermissions": [ "READ_CODE", "READ_VULNERABILITY" ], "baseAccessLevel": { "integerValue": 10, "stringValue": "GUEST" } } } } }

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.