Remote debugging of openlibrary site in docker

[cdrini]

Description

Feature. Allow for remote debugging the local site. Closes #2076 . Logging in doesn't seem to work with only 1 gunicorn worker (for some reason), so the flow is a bit awks, but I think still useful.

In action (sorry mouse is invisible):

Not crazy over the magic /attach_debugger endpoint; ideally I'd like to show a "Dev Tools" button visible on the homepage toolbar if the site is running locally, but not sure how to access configs from the template (if anyone has info on that). I think still this is worth merging as is, BUT WANT SOMEONE TO TRY IT BEFORE IT GETS MERGED. @hornc @mekarpeles One of you would be great candidates :)

Technical

This requires VS Code + its Python extension. To use:

1. docker-compose up -d as usual and login as admin. Then docker-compose down.
2. Open the repo in VS Code
3. Edit the last line of docker/ol-docker-start.sh to say workers 1 instead of 4
4. docker-compose up -d
5. Edit .vscode/launch.json:
   a. if using a docker machine (or docker toolbox), update host (run docker-machine ip)
   b. on Windows, I had to change localRoot to be c:/Users/MyUser/openlibrary/; if you get "file not found" errors, you might have to do the same.
6. Go to http://localhost:8080/admin/attach_debugger (or whatever your docker ip is) and click "Start"
7. Go to the debug panel (Ctrl+Shift+D) in VS Code, and click "Python: Attach"
8. Debug!

[brad2014]

Before merging/closing this, can we find a home in the wiki or in a repo md file to document this feature?

[cdrini]

Added a page here/to the sidebar: https://github.com/internetarchive/openlibrary/wiki/Debugger