CLI args as proxy syntax

```sh
lspcat \

{mutantlang}! --completion -- lsp-server-a --some-flags \
! lsp-server-b \
! --lang jsx --inlay-hints -- lsp-served-c \
! --filter "some regex" --completion "cli-app --some-flags" \

{rescript}! --completion "rescript-editor-analysis.exe completion "
```
- `!` represent pipe, similar to gstreamer
- `--` split between lspcat args and lsp-server args. Yes, it's _that_ GNU convention.
- `--lang language-id` tell the incoming language-id (sometimes used by lsp-server to switch between different language i.e `deno lsp` differentiate between javascript and jsx)
- `{language-id}!` tell which proxy to use when code editor open a file

---
Reference
- GNU netcat or NMap ncat
- websocat
- other *cat? 🐈
- not *cat 😹, but gstreamer `!` (pipe) syntax might be handy for solving #4