Background
---
When a git repository is hosted in multiple GitLab instances the
`.goreleaser.yml` needs to take in consideration both APIs endpoints. At
the moment it defaults to GitLab.com and you can override it with
`gitlab_urls` however this forces you to only support 1 GitLab instance.

We need this for
https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/14122
where we have a tool that is developed on GitLab.com but then mirrored
to an internal GitLab instance since we need it to operate GitLab.com
even when it's down.

Solution
---
Support templates like `{{ .Env.CI_SERVER_URL }}` for the
`gitlab_urls`, `github_urls`  and `gitea_urls` so it can use environment
variables and the same `.goreleaser` file can be used in multiple SCM
instances.