Fixes #200 - Add an ability to import core bugs as kb bugs

[ksy36]

This will import core bugs that have webcompat:platform-bug and a blocking breakage report as Knowledge Base bugs (saves a relation in breakage_reports table)

Checklist for reviewer:

• [ ] Commits should reference a bug or github issue, if relevant (if a bug is referenced, the pull request should include the bug number in the title)
• [ ] Scan the PR and verify that no changes (particularly to .circleci/config.yml) will cause environment variables (particularly credentials) to be exposed in test logs
• [ ] Ensure the container image will be using permissions granted to telemetry-airflow responsibly.

[ksy36]

r? @jgraham @scholtzan

[ksy36]

Thanks!