[galargh]

Related to #127

It adds tests for access control, batch uploads, and service termination (parts of what was mentioned in the issue). Also, as suggested there, it keeps the longer running tests optional - they can be enabled via run-optional-scenarios label.

I added labeled/unlabeled events to the CI workflow so that adding/removing the optional scenarios label would trigger them immediately. These tests are quite expensive in general so if we start using labels more here we might want to consider removing that auto-trigger. Then, the rerun would have to be forced via close/reopen PR or pushing an empty commit for example.

Added scenarios:

• Negative permissions: requests from another user and/or with invalid data are rejected without changing the data set
• Bulk add (optional): uploads 40 distinct pieces in one batch, then checks the count and looks for each piece
• Termination controls (optional): checks provider-relayed and direct termination, fees, etc.