Allow loading python processors from a git repository in NiFi 2.0

[soenkeliebau]

NiFi 2.0 adds support for python processors that can be used in flows.
These can be loaded by simply providing them in a directory on the pod and configuring NiFi to look into this directory.
NiFi also supports hot reloading of these processors out of the box, so this would be a perfect use case for a git-sync sidecar container, like we are using for Airflow already.

Tasks

Beta Give feedback

1. Allow specifying a gitsync sidecar container (potentially with multiple repos)
2. Mount repositories into the pods
3. Configure NiFi to load processors from these mounts