Add devcontainer configuration and CI

[Schamper]

Add a basic devcontainer configuration and CI to pre-build it. Other Dissect projects can re-use it like so:

{
	"name": "Dissect",
	"image": "ghcr.io/fox-it/dissect-devcontainer",
	"postCreateCommand": "pip3 install --user --editable . --config-settings editable_mode=compat"
	// Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
	// "remoteUser": "root"
}

Or '.[dev]' is that project has one.

[Miauwkeru]

some changes that I just spotted

[Miauwkeru]

If we add pull_request to the on: too, we can have a pipeline for the PRs and see if it actually succeeds in building the image. In the case we make changes to the whole things

[Miauwkeru]

LGTM