Use the Taskcluster Python client rather than direct http requests

[ahal]

Currently we just make manually crafted API requests to the TC endpoint rather than going through the Taskcluster Python client. This has been working fine for a long time, but we are likely missing out on some robustness and could push some complexity out of Taskgraph.

But the bigger reason to consider switching soonish, is that we want to start using the object service in Firefox CI. The official clients all already support artifact verification out of the box. If Taskgraph were using the Python client, it would start getting the benefit of artifact integrity as soon as things start switching over to the object service.

[gabrielbusta]

I've got a couple of questions about this.

If we switch now, would we get the benefits provided by the object service?

When we do this, can we simplify some stuff in the scriptworker CoT?

[ahal]

I've got a couple of questions about this.

If we switch now, would we get the benefits provided by the object service?

We'd need to start using it on a pool by pool basis, but yes! It'll require an up to date generic worker in the images (no docker worker) and updated task definitions to support it (likely other taskgraph changes).

When we do this, can we simplify some stuff in the scriptworker CoT?

Yep! We can stop storing artifact hashes in the CoT.json.