eww: added improvements

[Eveeifyeve]

Description

• Added systemd option to run eww as a service inspired by programs.waybar.systemd
  • Removes the need of this pr: services.eww: init #5136
• Added string config option implements this propperly eww: string based config #5585
• Deprecates configDir instead use the string config options configYuck & configScss
• Made configYuck, configScss & configDir optional. which does this: eww: make configDir setting optional #4595

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.

Maintainer CC

@mainrs

[Eveeifyeve]

Also @mainrs, please provide an actual email not a GitHub nore-reply because I can't contact you sept for here about this.