Add Elixir LS to "Known compatible LSP servers" wiki page

[fuelen]

Please include the following LS for Elixir

• https://github.com/elixir-tools/next-ls
• https://github.com/lexical-lsp/lexical

both servers support progress

[j-hui]

Thanks for bringing this up! I just added next and lexical to the page.

The name of your issue says "Elixir LS"---is that referring to elixirls specifically as well or just the two other Elixir servers you mentioned? (As far as I'm aware, elixirls still doesn't support LSP progress, according to this issue)

[fuelen]

By using "Elixir LS" I just wanted to say "Elixir language servers" 🙂 No referring to elixirls. Sorry for the confusion.
And thank you for updating the wiki