Switch default langserver for ocaml to ocamllsp

Switch default langserver for ocaml to ocamllsp

The repo for ocaml-language-server has been archived and inactive
for quite some time:

   https://github.com/ocaml-lsp/ocaml-language-server

Meanwhile, ocaml-lsp is the generally-preferred option, and is actively
maintained in the ocaml org itself:

   https://github.com/ocaml/ocaml-lsp/

* eglot.el (eglot-server-programs): switch caml-mode  entry.

GitHub-reference: close https://github.com/joaotavora/eglot/issues/677