feat(stresstest): TTL after 1h and make cleanup configurable

[jan-auer]

Stresstests are frequently canceled or crash as we test objectstore's limits.
This leaves objects in the backends permanently. To fix this, we now configure a
default 1h TTL for all objects created by the stresstest.

Since we can usually rely on that TTL, we no longer have to run the cleanup.
This saves significant time, as the deletions usually take longer than the test
itself.

To make configuration and usage a bit easier, the stresstest is now converted to
the command pattern.