Fix for ignored forge URL when using APIv3

Repo for APIv3 is using PuppetForge as API client. PuppetForge is using https://forgeapi.puppetlabs.com remote URL by default. So, if you set custom forge URL in Puppetfile and run librarian-puppet with --no-use-v1-api, it will ignore your forge URL and use official forge.

I have added constructor for repo v3 which sets PuppetForge remote URL.

@rodjek, are you interested in merging this?