Integration: Bitbucket

[bhirsz]

Provide integration with Bitbucket code insights.

I've done initial research and I see that Bitbucket only supports uploading results 'manually' by using their API.

We can:

1. Create bitbucket report that will produce report.json and annotation.json which users can upload on their own (in their script)
2. Additionally create small util that can be run to upload results through API

For API we need libraries such as request or similar. Since we only need to POST to two endpoints we don't need bitbucket python library etc. It could be added as separate pypi mode (pip install robotframework-robocop[bitbucket]).

Official documentation:

https://developer.atlassian.com/server/bitbucket/tutorials-and-examples/code-insights-tutorial/
https://docs.atlassian.com/bitbucket-server/rest/7.9.0/bitbucket-code-insights-rest.html