Use bash as default shell in Dockerfile
GitPod's VSCode in browser (and probably others?) defaults to use `$SHELL` in integrated terminal, which is `sh`.
This change is just confort to have it open `bash` without having to change the settings or open the right one manually.

Note that the `.devcontainer` setting should not be necessary anymore, as the algorithm to chose the right shell should be the same for GitPod and VSCode remote.

From the [relevant VSCode doc](https://code.visualstudio.com/docs/terminal/profiles):
> The default terminal profile shell defaults to `$SHELL` on Linux and macOS and PowerShell on Windows. VS Code will automatically detect most standard shells that can then be configured as the default.


**EDIT**
Added a couple of bonus points:
- `--install-hooks` in pre-commit. This will configure everything immediately. Otherwise, the first commit will be very slow (pre-commit creates the environments on-demand, this will force the creation at the first start)
- `bash-completion`. So to <TAB> everything (git completion works out of the box, for example)
Thanks @serl these are nice changes. I don't think very many core developers are using this at the moment, so if you run into issues feel free to keep pushing up PRs. Would be great to improve Hello @WillAyd, thanks for the fast reply!

Yes I think there'll be more to do (looking at https://github.com/pandas-dev/pandas/issues/59459). I'm not really familiar with the project yet, so if you have advices on that issue, I'd be grateful (otherwise I'll crawl my way in 🦝) Thanks @serl . I also do not use Gitpod so am not up to speed on what may or may not be working with it. If you use it and run into problems, I would just continue to create an issue for the buggy behavior (or find one, if it already exists) and can get directed feedback from there