Add more useful information in autocompletion results

Ale is a great vim plugin and I have been happily using it for a while. I am experimenting with its code completion functionality recently. One thing I notice is that the popup menu for C-family languages does not have the function signature. The attachment is the result of code completion in a cpp file using Ale's omnifunc and `clangd` as the linter:

While I can see the type of the completed keyword, I don't have any information about the function argument list. I also tried [vim-lsp](https://github.com/prabirshrestha/vim-lsp) with `clangd` and the result is shown below.

As can be seen, `vim-lsp` provides the user with the complete function prototype which could be extremely useful for complicated functions. I am wondering if the same thing can be implemented in ale. If it is already part of ale, can you elaborate a bit how to enable it?