TOP-1250: Decorate tests with Xray test identifiers

This adds the pytest-jira-xray plugin to automatically publish test results to Xray. Some additional work was done to automatically upload attachments as test evidence.

Note that publishing to Xray is currently not done automatically. This story was a timeboxed investigation and finishing the Xray integration will be done in a later sprint.

Here's an example of the result so far: https://jira.skatelescope.org/browse/CLT-40