erlang: Add support for installing elp language server (#14923)

This PR updates the Erlang extension with support for installing the
[Erlang Language
Platform](https://github.com/WhatsApp/erlang-language-platform) (`elp`)
language server from the GitHub Release assets.

Release Notes:

- N/A

assets/settings/default.json

@@ -743,6 +743,9 @@
     "Elixir": {
       "language_servers": ["elixir-ls", "!next-ls", "!lexical", "..."]
     },
+    "Erlang": {
+      "language_servers": ["erlang-ls", "!elp", "..."]
+    },
     "Go": {
       "code_actions_on_format": {
         "source.organizeImports": true