Consider adding CodeClimate and/or other code coverage reporting tooling to dev container config

[toolness]

At https://github.com/JustFixNYC/tenants2/pull/2040#discussion_r615044115 @samaratrilling was able to get a code climate extension running in vscode, which was neat because it showed the coverage information in her VSCode rather than requiring her to go to a website to see it.

It might be useful to have this extension in our devcontainer.json. It would also be cool if it could look in our coverage folder for the coverage information, so that we could just re-run the test suite locally in order to see the latest coverage statistics rather than having to push to github. (We can currently look at the HTML files in the coverage folder but it's a hassle.)