feat: use `user_name/repo_name` instead of the `user_latex_repo_url` to find user LaTeX repository

[ycexiao]

Problem

It comes from the conversation in #46.

Entering user_name/repo_name is a lot shorter than entering the URL. It also helps to reduce typos when users enter the values.

Proposed solution

Add config for package create manuscript. E.g. Add package config user.repo_platform gitlab for gitlab users and package config user.repo_platform github for GitHub users.

Then, assemble the correct repo URL from user_name /repo_name

[sbillinge]

I would prefer this to be entered at one prompt not two. Could we ask for org_name/rep_name and not have them separate?