Add devcontainer settings

[mariocynicys]

devcontainer settings are used to define an environment for the project when it runs on github codespaces. This commit will cause new codespaces to start with Rust and cargo preinstalled.

This will allow others to easily spin up a development environment for the project quicker (and does help me when I don't have my laptop on me and need to try something out/ do quick review :) ).

[mariocynicys]

Better also install bitcoind and tor inside the container.