Make apache-airflow not required

[tomasfarias]

Since we wish to support all MWAA supported versions of Airflow,
this requires supporting both 1.10.12 and 2.X releases. However, There
are several conflicting dependencies between dbt-core and
apache-airflow. None of the conflicts should break us, but they do
make dependency resolution impossible, which means airflow-dbt-python
cannot be installed.

For this reason we have removed the dependency to
apache-airflow. Assuming that as an Airflow operator we are always
installing airflow-dbt-python in an environment that already has
Airflow installed, this shouldn't cause any issues in production
deployments.

Moreover, this makes testing multiple Airflow versions easier as we
can pre-install apache-airflow.

[codecov]

Codecov Report

Merging #35 (32115a2) into master (08f0125) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #35   +/-   ##
=======================================
  Coverage   96.16%   96.16%           
=======================================
  Files           5        5           
  Lines         678      678           
=======================================
  Hits          652      652           
  Misses         26       26           

Flag	Coverage Δ
unittests	96.16% <ø> (ø)

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[tomasfarias]

The likelihood of this breaking somebody's environment is low as it's very reasonable to assume Airflow deployments already have, well, Airflow installed. But, I may be missing so we'll leave this one open for a bit.

[nugic]

I like your project @tomasfarias !
Was trying to get airflow-dbt-python working on Astronomer, but during the build conflicts came up due to apache-airflow version requirements (Astronomer uses their own airflow builds with version epoch-s).
So this was exactly what was needed, pulled the branch and installed airflow-dbt-python without airflow and seems to work perfectly.
Thanks again and hope it gets released soon!

[tomasfarias]

Hey @nugic. Awesome comment! Thanks for letting me know! I was hoping to get some confirmation that this is a needed change as it's also affecting our MWAA setup. Now I'll definitely merge this and release it shortly.