Pass Gitlab auth_token to packages listed in Remotes

[overmar]

When install_gitlab has to install packages from the remotes line, it loses its auth_token, this allows the auth_token to persist in the ... and be recalled when necessary

[bestdan]

I think this might solve this issue for github too:
#295

Any reason to not make both changes in this PR?

[antoine-sachet]

This may have unintended consequences, just like PR #145 introduced #337.

This works when the dependency needs the same host, user, password, auth_token, etc. But what if it does not? Then you've just broken the installation by passing the wrong host. Even if you just pass the credentials, you may pass the wrong credentials: imagine a gitlab package with a dependency on a github package, it will use the wrong auth_token.

You can easily pass credentials to the dependencies using environment variables (and it won't pass the wrong credentials), so there is no need for this in the first place. A better solution would be a useful message if private dependencies are detected/suspected.

By the way, credentials are already passed to the dependencies (since #145, see below).

combine_deps(
    package_deps(deps, repos = repos, type = type),
    remote_deps(pkg, ...)) # credentials passed to remote deps here

package_deps does need access to the repo to check the version but in any case the result is discarded since combine_deps will keep the remote from remote_deps... so does package_deps really need the sha of the remote commit?