[PR] Make `graphviz` dependency optional [airflow]

["potiuk (via GitHub)" <gi...@apache.org>]

potiuk opened a new pull request, #36647:
URL: https://github.com/apache/airflow/pull/36647

   The `graphviz` dependency has been problematic as Airflow required dependency - especially for ARM-based installations. Graphviz packages require binary graphviz libraries - which is already a limitation, but they also require to install graphviz Python bindings to be build and installed. This does not work for older Linux installation but - more importantly - when you try to install Graphviz libraries for Python 3.8, 3.9 for ARM M1 MacBooks, the packages fail to install because Pythonn bindings compilation for M1 can only work for Python 3.10+.
   
   There is not an easy solution for that except commenting out graphviz dependency from setup.py, when you want to install Airflow for Python 3.8, 3.9 for MacBook M1.
   
   However Graphviz is really used in two places:
   
   * when you want to render DAGs wia airflow CLI - either to an image or directly to terminal (for terminals/systems supporting imgcat)
   
   * when you want to rended ER diagram after you modified Airflow models
   
   The latter is a development-only feature, the former is production feature, however it is a very niche one.
   
   This PR turns rendering of the images in Airflow in optional feature (only working when graphviz python bindings are installed) and effectively turns graphviz into an optional extra (and removes it from requirements).
   
   This is not a breaking chnage technically - the CLIs to reder the DAGs is still there and IF you already have graphviz installed, it will continue working as it did before. The only problem when it does not work is where you do not have graphviz installed it will raise an error and inform that you need it.
   
   Graphviz will remain to be installed for most users:
   
   * the Airflow Image will still contain graphviz library, because it is added there as extra
   * when previous version of Airflow has been installed already, then graphviz library is already installed there and Airflow will continue working as it did
   
   The only change will be a new installation of new version of Airflow from the scratch, where graphviz wlll need to be specified as extra or installed separatley in order to enable DAG rendering option.
   
   Taking into account this behaviour (which only requires to install a graphviz package), this should not be considered as a breaking change.
   
   Extracted from: #36537
   
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Re: [PR] Make `graphviz` dependency optional [airflow]

["potiuk (via GitHub)" <gi...@apache.org>]

potiuk merged PR #36647:
URL: https://github.com/apache/airflow/pull/36647


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