fourmolu: init at 0.14.0.0

`fourmolu` is a configurable fork of `ormolu`, and it's one of the more
common Haskell formatters (used by `cabal-install` among other
projects). This adds a top-level derivation for it.

pkgs/by-name/fo/fourmolu/package.nix

···
+{
+  haskellPackages,
+  haskell,
+}:
+
+let
+  inherit (haskell.lib.compose)
+    justStaticExecutables
+    ;
+in
+justStaticExecutables haskellPackages.fourmolu