Use completion item detail in completion renderer

[krassowski]

Completion item provides detail property which includes language-specific detail information about the completion, e.g. the module from which a function was imported.

1. It should be displayed by default instead of type text if available (the type is already shown by the icon); We can modify the <li> element with the completion item after its creation, or modify how it is created here:

   https://github.com/krassowski/jupyterlab-lsp/blob/d8b670528605f4f736da08c965c42b82688d0981/packages/jupyterlab-lsp/src/features/completion/completion_handler.ts#L137

2. the user should be able to choose what they want to be displayed (maybe there options: detail, type, whichever available); this can happen later, but the access to settings in the renderer is already possible using the this.options.integrator.settings:

   https://github.com/krassowski/jupyterlab-lsp/blob/d8b670528605f4f736da08c965c42b82688d0981/packages/jupyterlab-lsp/src/features/completion/renderer.ts#L78

   to add a new setting one should modify the schema/completion.json file and follow with jlpm build:schema from the repository root.

3. the resolve request needs to be updated to copy the detail from response, as is the documentation here:

   https://github.com/krassowski/jupyterlab-lsp/blob/d8b670528605f4f736da08c965c42b82688d0981/packages/jupyterlab-lsp/src/features/completion/renderer.ts#L25