fix(nvim): re-add intelephense

Phpactor isn't providing LSP information or diagnostics within Drupal
tests whereas Intelephense does.

This means that I'm getting duplicate results in files where both
Intelephense and Phpactor are working, but I'll look into this again and
see if I can go back to using just Phpactor.

lua/opdavies/lsp/init.lua

@@ -28,6 +28,7 @@ lsp.setup_servers({
   'cssls',
   'dockerls',
   'html',
+  'intelephense',
   'jsonls',
   'nixd',
   'phpactor',