Change ModeChanged autocmd to InsertEnter

ModeChanged '[^i]*:i' still triggers too often, when not required.
Tested with InsertEnter and it works as expected, but I do remember that
I have choosen ModeChanged in first place because InsertEnter wasn't
triggered after opening neovim and first entering insert mode, but now
it works.

lua/neocodeium/init.lua

@@ -119,8 +119,7 @@ local function enable_autocmds()
       end,
    })
 
-   create_autocmd("ModeChanged", {
-      pattern = "[^i]*:i",
+   create_autocmd("InsertEnter", {
       callback = function()
          completer:initiate()
       end,