Allow further configuration by using git config names

[UnFefeSauvage]

Summary of the new feature/enhancement

In the extension settings, you could use git config names instead of "userName" and "email".

This could ease adding new settings to the profiles and would remove the need to translate fields to git config names
("userName" -> "user.name")

Then, to identify profiles, you could generate an id or use the profile label and put it as a custom field in the user config.

Proposed technical implementation details (optional)

The updated config format could look something like that:

{
  "label": "My profile",
  "config": {
    "user.name": "Alice Bob",
    "user.email": "alice.bob@example.de"
  },
  "selected": true
}

And could, for example, be updated by a user this way to configure GPG signing as well:

{
  "label": "My profile",
  "config": {
    "user.name": "Alice Bob",
    "user.email": "alice.bob@example.de"
    "user.signingkey": "ABCDEF0123456789BD",
    "commit.gpgsign": true
  },
  "selected": true
}

The id could be stored this way in .git/config:

[user]
  name = Alice Bob
  email = alice.bob@example.de
[gcup]
  profileId = My profile

We might want to validate config names, a regex like this one (untested) ^([a-zA-Z0-9]+\.?)+[a-zA-Z0-9]$ should do the trick.

Also, when switching profiles, we would have to remove each field of the previous profile before applying the new one.

I might look into it myself and make a pull request but I'm not familiar with TypeScript.