Enable Decomposed database RSpec jobs to run at a schedule

We introduced new RSpec jobs that run in decomposed database mode in this MR: !68232 (merged) - the jobs only run when a merge request has the ~"pipeline:run-decomposed" label.

Proposal

When the jobs are stable, we should start running these decomposed database jobs at a regular schedule

Open questions

1. Do we wait until the decomposed jobs are all green ?
2. If we start running the decomposed jobs when there are still some failures, how will we track and report the total number of failures ?

/cc @craig-gomes @tpazitny