Convert garbage collection system tests to invoke per table

[patchwork01]

Background

Split from:

• Enable schedule rules by default in system tests #3722
• Extend ParallelCompactionsST to expose wait for input file assignment problem #3631

Description

When we explicitly invoke garbage collection in system tests, we'd like to send a message per table of the current system test instead of invoking the trigger lambda.

This should allow us to run tests with an offline table, so that we can take control of the order things happen without needing to pause the whole instance.

This should make it easier to parallelise tests, and to convert other tests to rely on scheduled rules.

Analysis

See the parent issue for details of general code changes for schedule rules in system tests.