Create new entity called TriggerVariablesEnitity for trigger variables,
to aid reuseablity in the future.
Update JSON schema to include trigger information in the response.
Refactor rspec tests a bit to reduce duplication and for the `context`
to make sense.
closes https://gitlab.com/gitlab-org/gitlab-ce/issues/50989
Start validating against the exciting JSON schema for the job controller JSON
response.
The JSON schema is not complete since there is quite a lot missing, this will
be done in a separate issue.