Move first provider (airbyte) to a separate project

[potiuk]

This is the first step to move providers to separate projects inside our monorepo.

Airbyte is a first provider that is separated out to a project under "providers/<PROVIDER_ID>" directory. This has the nice property that all files belonging to the same provider are under a single directory that is part of the Airflow workspace. For now the code is more complex because we are handling providers being in either "old" or "new" structure, but once we move old providers to the new structure, a lot of code could be removed and simplified.

The new structure for provider code is:

providers
        |- PROVIDER_ID
        |            |- src
        |            |    |-airflow
        |            |            |- providers
        |            |                       |- PROVIDER_ID
        |            |- tests
        |            |      |- providers
        |            |                 |- PROVIDER_ID
        |            |- docs
        |            |     |- .latest-doc-only-changes.txt
        |            |- pyproject.toml
        |            |- CHANGELOG.rst
        |            |- provider.yaml
        |            |- README.rst
        |- PROVIDER_ID2
        ...

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[potiuk]

This is not yet complete, and I also extract some things out of that to separate PR to make it smaller/simpler. Just wanted to test the image build process.