[AIRFLOW-5292] Allow ECSOperator to tag tasks

[philipphoffmann]

This commit introduces a parameter for the ECSOperator in order to
pass along tags to any tasks it is running.

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[ashb]

I know this is how the boto API accepts tags, but might it be easier for users to instead accept a dict as {'tagKey':, 'tagValue'}?

[philipphoffmann]

yup, sounds good, changed it