add explicit formatter for cue (#5679)

cuelsp does not support formatting.
Cue language support was added to Helix before
"formatter" was available.

References:
https://github.com/helix-editor/helix/pull/3262
https://github.com/dagger/cuelsp/issues/44

languages.toml

@@ -1778,6 +1778,7 @@ auto-format = true
 comment-token = "//"
 language-server = { command = "cuelsp" }
 indent = { tab-width = 4, unit = "\t" }
+formatter = { command = "cue", args = ["fmt", "-"] }
 
 [[grammar]]
 name = "cue"