Move docker decorator example dag to docker provider

[ephraimbuddy]

This example dag errors out during startup when we set AIRFLOW__CORE__EXAMPLE_DAGS=True and docker
provider is not installed.

---

^ Add meaningful description above

Read the Pull Request Guidelines for more information.
In case of fundamental code change, Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in UPDATING.md.

[kaxil]

We should leave the virtualenv task here and separate out the docker task into a separate example DAG in it's provider

[github-actions]

The PR most likely needs to run full matrix of tests because it modifies parts of the core of Airflow. However, committers might decide to merge it quickly and take the risk. If they don't merge it quickly - please rebase it to the latest main at your convenience, or amend the last commit of the PR, and push it with --force-with-lease.

[kaxil]

one test failed: https://github.com/apache/airflow/pull/18739/checks?check_run_id=3804973532#step:10:1485

[ephraimbuddy]

Hi @potiuk , this failure seems related to DockerDecorator not usable in airflow versions less than 2.2.
It is failing at import_all_provider_classes on airflow 2.1 for install from wheel but passing for sdist

[potiuk]

Hi @potiuk , this failure seems related to DockerDecorator not usable in airflow versions less than 2.2. It is failing at import_all_provider_classes on airflow 2.1 for install from wheel but passing for sdist

Yep. This is precisely what is expected. The problem is that we try if "ALL" provider code imports nicely for 2.1 without errors - including the examples. In this case we've made a deliberate decision to move the example to "docker" provider, even if it will not work for 2.1. This is fine, so the solution is to try/except the example to get example_dag import without the exception (with appropriate comment).

[ephraimbuddy]

Hi @potiuk , this failure seems related to DockerDecorator not usable in airflow versions less than 2.2. It is failing at import_all_provider_classes on airflow 2.1 for install from wheel but passing for sdist

Yep. This is precisely what is expected. The problem is that we try if "ALL" provider code imports nicely for 2.1 without errors - including the examples. In this case we've made a deliberate decision to move the example to "docker" provider, even if it will not work for 2.1. This is fine, so the solution is to try/except the example to get example_dag import without the exception (with appropriate comment).

Done. Please take a look