Generate test reports for bitbucket

[nathanjmcdougall]

Motivation
There is a special bitbucket support for parsing test reporting. We should support this.

https://community.atlassian.com/t5/Bitbucket-questions/Bitbucket-Pipelines-with-pytest-XML-report/qaq-p/874636

Could be as simple as adding --junitxml=test-reports/report.xml to the pipeline. Can this config be added to pyproject.toml though? Is that even sensible since we might prefer to not generate the reports locally and only on CI? A bit of thought needed on this point.

Summary of desired enhancement
Support Bitbucket's native test reporting functionality.