Feature/transposition geom extraction

[nick-j-roberts]

Minor cleanups to repo

• deletes useless general requirements.txt
• adds plugin and etl specific .env.sample files with only required entries, specifies these in the docker compose file

Adds new ETL for extracting a geojson file of the valid transposes for a watershed provided by user input

• adds script and requirements.txt for script dependencies
• adds dockerfile and compose service for etl