[AIRFLOW-5180] Added static checks (yamllint) + auto-licences for yaml

[potiuk]

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[potiuk]

Part of static checks dealing with yaml (yamllint + consistent licenses). Removed the chaing of depnding commits.

[potiuk]

Rather small consistency change for all yaml files :). Would be nice to merge it.

[ashb]

One minor change, otherwise looks good to me.

Do we need to add yamllint-config.yaml to the safelist in .dockerignore?

[potiuk]

@ashb - no, we do not need to add it. yamllint static check is not run in Docker.

But we should add it as pre-requisite (just did)

      - id: yamllint
        name: Check yaml files with yamllint
        entry: yamllint -c yamllint-config.yml
        language: python
        types: [yaml]
        exclude: ^.*init_git_sync\.template\.yaml$|^.*airflow\.template\.yaml$

It would work out-of-the-box if we did not have [devel] extra.

The key is 'language: python' here. In this case Yamllint is run via yamlint python pre-commit plugin. Those plugins (which are python-based) manage their dependencies and virtualenvs on their own. Basically those built-in plugins create their own small virtualenv where they install needed dependencies (yamllint in this case) using pip install . and run the plugin within that virtualenv. It's all done automagically by the pre-commit framework - without docker. This works for simple stand-alone plugins like yamllint where you have just one or two dependencies that are system-independent and can rely on virtualenv. In our case yamllint is only installed with [devel] extra so we need to add it as pre-requisite to be installed locally (it will complain if yamllint is not installed)