Support gitlab releases

[xomaczar]

No description provided.

[rwjblue]

👋 - I don't currently have any projects using GitLab, but this definitely seems like a thing we can support!

release-it (which is where most of the work for actual releases) already has support for GitLab based releases (documentation here). I think the work to do in this repo would be to detect the remote type (github, gitlab, etc) likely based on the git configuration and for gitlab:

• disable labels modification (there may be a corollary in GitLab land)
• update the release-it configuration to use GitLab instead
• update the RELEASE.md template to mention gitlab
• figure out what to do RE: lerna-changelog supporting gitlab (doesn't currently support anything but github)