feat: add the cabal-fmt formatter (#318)

README.md

@@ -195,6 +195,7 @@ You can view this list in vim with `:help conform-formatters`
 - [blue](https://github.com/grantjenks/blue) - The slightly less uncompromising Python code formatter.
 - [buf](https://buf.build/docs/reference/cli/buf/format) - A new way of working with Protocol Buffers.
 - [buildifier](https://github.com/bazelbuild/buildtools/tree/master/buildifier) - buildifier is a tool for formatting bazel BUILD and .bzl files with a standard convention.
+- [cabal_fmt](https://hackage.haskell.org/package/cabal-fmt) Format .cabal files preserving the original field ordering, and comments.
 - [cbfmt](https://github.com/lukas-reineke/cbfmt) - A tool to format codeblocks inside markdown and org documents.
 - [clang_format](https://www.kernel.org/doc/html/latest/process/clang-format.html) - Tool to format C/C++/… code according to a set of rules and heuristics.
 - [cljstyle](https://github.com/greglook/cljstyle) - Formatter for Clojure code.

lua/conform/formatters/cabal_fmt.lua

@@ -0,0 +1,8 @@
+return {
+  meta = {
+    url = "https://hackage.haskell.org/package/cabal-fmt",
+    description = "Format cabal files with cabal-fmt",
+  },
+  command = "cabal-fmt",
+  stdin = true,
+}