Nersc deployment adaptations (Auth, Environment variables)

[Wiebke]

This PR groups some minor changes in relation to the deployment on Nersc. Most importantly it adds the basic auth wrapper, for now with a single username-password pair.

Additionally the following minor changes are included:

• Rename API_KEY to TILED_API_KEY to prepare for adding other keys (e.g. to Splash ML)
• Update the TILED_URI to https://tiled-seg.als.lbl.gov in README.md
• Make it possible for EXPORT_FILE_PATH to be an environment variable
• Add missing volume mount for constants.py in docker-compose.yml
• Ignore differently named Python environments *env/

[github-actions[bot]]

Staging application has been deployed and is available at: https://dash5-services.plotly.host/ml-exchange-staging Production app name: ml-exchange Current branch name: nersc-deployment-adaptations Commit: be7f17668e6c9b3d3c83eead882e75e868a65117