Send commit statuses to GitLab, Bitbucket, and GitHub Enterprise

[jankeromnes]

Is your feature request related to a problem? Please describe

We currently have this support matrix:

Integration	Can create Project	Push triggers Prebuild	Prebuild sets Commit Status
github.com	✅	✅	✅
GitHub Enterprise	✅	✅	❌
gitlab.com	✅	✅	❌
Self-Managed GitLab	✅	✅	❌
bitbucket.org	✅	✅	❌
Bitbucket Server	✅	✅	❌

Describe the behaviour you'd like

This issue is about making the rightmost column green:

• Send prebuild commit statuses to both gitlab.com and Self-Managed GitLab (via the API)
• Send prebuild commit statuses to bitbucket.org (via the API)
• Send prebuild commit statuses to GitHub Enterprise (via the API)

Describe alternatives you've considered

Additional context

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.