Support `dprint` custom formatter options

[dephiros]

Is your feature request related to a problem? Please describe. I am trying to see dprint file association for this plugin: https://github.com/g-plane/markup_fmt which requires markup config. Error:

       error: The option `programs.dprint.settings.markup' does not exist. Definition values:
       - In `/nix/store/3gchkgvjabjq2b8jblmzwcczq68z9613-source/treefmt.nix':
           {
             associations = [
               ".html"
               ".svg"
               ".mustache"
           ...

https://dprint.dev/config/#associations

Describe the solution you'd like A way to specify dprint extra config

Describe alternatives you've considered

🤔

Additional context

[zimbatm]

/cc @gkze