Add devcontainer support

[loujaybee]

Example:
https://github.com/glebbash/lole-lisp/tree/main/.devcontainer
gitpod-io/gitpod#7721 (comment)

[loujaybee]

Run tasks on start:

https://stackoverflow.com/questions/69892318/task-in-tasks-json-doesnt-auto-start-in-a-vscode-dev-container