Use config file instead of editing source code

[Leonidas-from-XIV]

This PR changes the way Sandworm is reconfigured by moving from editing sourcecode as part of an GH workflow into using a config file.

Some notes about it:

• It uses TOML. No particular significance about the format. The OCaml implementation seems to be well-maintained and the format is reasonably accepted. Could have used INI files as well, but the OCaml implementation is less mature.
• This PR gives up on the "staging" branch setup. It is easier to have a single main branch and have test as an option to its execution. We need to rework how to test things in either case.
• The config options are taken from the workflow

Closes #199