build: Add devcontainer

[pythoninthegrass]

Hi @alkrauss48 !

Was spitballing with @laylark on getting a dev environment up and running for the simple slides repo.

MS has a cool built-in feature with VSCode called development containers. I'd be happy to set this up so that it leverages your existing compose file.

It also installs your recommended extensions automatically lowering the barrier to entry for devs who are either new to the stack or don't have everything installed locally.

Lmk what you think!