Expand parameters for commit status API endpoint
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### Problem to solve
We use buildbot for our testing infrastructure. It would be nice if we could provide things like a custom stage string, a retry_url, trigger warnings, set tags, and set things like `:allow_failure` for our builders.
### Proposal
I'm thinking of these additional optional parameters to the `POST` for the commit status API endpoint:
- allow_failure (bool)
- tags (list of strings)
- show_warning (bool)
- cancel_url (string)
- retry_url (string)
- download_url (string)
A field for an additional link (say, to documentation hosted for the build or some other bit specific to whatever CI setup there is) would be nice as well.
issue