Improve the dependency handling

[zheyu-wang-tony]

There might be dependency between the single fields and the fields within a model. Right now, the PR supports the below two scenario:

1. single fields depend on the fields in a model.
2. a model depends on some single fields.

There's actually one case missing, which is single fields and model are depend with each other. We probably need to find a way to specify the dependency tree.

[zheyu-wang-tony]

@maoo Would you please help to check whether our setting bot really work? Since I can merge my PR without any review. However, from setting.yaml, I can see that:

  branches:
    - name: master
      protection:
        required_pull_request_reviews:
          required_approving_review_count: 1
          dismiss_stale_reviews: true
          require_code_owner_reviews: true
          dismissal_restrictions:
        required_status_checks:
          strict: true
          contexts: [ "verification/cla-signed" ]
        enforce_admins: true
        restrictions:
          apps: []
          users: []
          teams: [ "finos/datahub" ]

I will at least need one review? Or it's because I'm in some admin group?

[zheyu-wang-tony]

@grovesy this pr also remove the duplicate logic in generate_from_model and generate_from_model_single, and keep all the generation logic in generate_from_model_single only.