Bitbucket Pipelines build URL

Currently we do not have this value

https://stackoverflow.com/a/59461628/335583 suggests a possible way to generate it, requires testing.

It would be returned here https://github.com/codecov/uploader/blob/fbbf7283ee691a43d02c44c5af56d6a32ec654a7/src/ci_providers/provider_bitbucket.js#L15