mpdscribble: add module

[msyds]

Description

This PR adds the module services.mpdscribble based on the NixOS module of the same name.

Old feature request: #4963

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all or nix develop --ignore-environment .#all using Flakes.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • Added myself as module maintainer. See example.

[teto]

Looks like a valid candidate for HM. If anyone else could try this out and report back, it would be nice.