Add Dockerfile formatter support

[li1234yun]

When I save the dockerfile, the zed will use default prettier formatter. The prettier is not support dockerfile.

2025-12-01T07:47:53+08:00 ERROR [crates/editor/src/editor.rs:17754] RPC request FormatBuffers failed: default prettier instance failed to format buffer: UndefinedParserError: No parser could be inferred for file "/home/lzy/git/architecture/code/microservice/app/nav/Dockerfile". While handling prettier request: {"jsonrpc":"2.0","id":5,"method":"prettier/format","params":{"text":"..snip..","options":{"plugins":[],"parser":null,"filepath":"/home/lzy/git/architecture/code/microservice/app/nav/Dockerfile","prettierOptions":{"printWidth":80,"useTabs":false,"tabWidth":4},"ignorePath":null}}}

[li1234yun]

  "languages": {
    "Dockerfile": {
      "formatter": "language_server"
    }
  },

Adding the above configuration seems to work properly.