Add support to define Resources on DockerSwarmOperator

[guydriesen]

This PR adds the support for defining docker Resources to the DockerSwarmOperator.

Currently it's only possible to define a memory limit on the swarm service. With this PR it will be also possible to define a memory reservation as well as a cpu reservation and limits to the service.

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[boring-cyborg]

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[Taragolis]

Looks nice, could you add tests cases for that change?

https://github.com/apache/airflow/blob/main/tests/providers/docker/operators/test_docker_swarm.py

[guydriesen]

Sure, will have a look at it.

[boring-cyborg]

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