action #129412

Updated by mkittler about 1 year ago

### Motivation 
 Judging by the "group" of jobs with the biggest result size are jobs not in any group. We had a brief look at the retention behavior of job results of groupless jobs but were not sure about it. 

 ### Acceptance criteria 
 * **AC1**: We know whether and how the cleanup of job results of groupless jobs works. 
 * **AC2**: The cleanup behavior¹ is configurable (and *not* using some hard-coded time intervals). 
 * **AC3**: There is a unit test ensuring the cleanup behavior¹ actually works as intended. 
 * **AC4**: Documentation about the cleanup behavior¹ and is in accordance with what is actually happening. 

 ¹ The "cleanup behavior" of job results of groupless jobs specifically. 

 ### Suggestions 
 * Have a look at `ib/OpenQA/Task/Job/` (the code under "create temporary job group outside of DB to collect") and `lib/OpenQA/Schema/Result/`. 
 * ~~Remove Remove the mentioned code and check whether tests fail.~~ No tests fail after the removal. We need to add a new test. fail.