Develop a Python cross-language wrapper for Java BigTableIO

Java connector: https://github.com/apache/beam/blob/master/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigtable/BigtableIO.java

Documentation for developing Python cross-language transforms:

https://beam.apache.org/documentation/programming-guide/#1311-creating-cross-language-java-transforms

https://beam.apache.org/documentation/sdks/python-multi-language-pipelines/

Existing cross-language transform for Cloud Spanner might serve as a good example to follow.

https://github.com/apache/beam/blob/master/sdks/python/apache_beam/io/gcp/spanner.py

https://github.com/apache/beam/blob/a4e112974d8f3f51e646d9e714a4f8d456d69b4d/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/spanner/SpannerTransformRegistrar.java