Dockerize flask app, allow to download files from S3 from generated URLs

[denist-huma]

What does this PR do?

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• Dockerize flask app, allow downloading files from S3 via temporary URLs

Description of Task to be completed?

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all the salt is in commit messages:

30bbb2c (HEAD -> dockerize, origin/dockerize) ref: create a temporary directory using the context manager 631a11d ref: no download_file, use root web path since it is a one page app 3af3d6a feat: Serve static files in Flask from private AWS S3 bucket 55b22a5 feat: way to run in docker container 74698eb improvement: update python version 3.8 c13a9a3 feat: set bucket name passing env f617f57 fix: should not mask errors 2c101ef fix: should run app with "flask run"

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