Introduce DEBUG workflow with minimum set of parameters and fake job to simplify debugging process

[vkuznet]

Impact of the new feature
In order to test entire chain of services in WMAgent it would be extremely useful to create a very basic, simple workflow JSON which will only contain one or few events, and fake CMSSW job, no input/output data, etc. Such workflow should have high priority in a system to process quickly and since they will not require input/output no staging should be done and it can be run on any site w/o issue (may be we can even have a fake site).

Is your feature request related to a problem? Please describe.
This feature request can be helpful help in reverse engineering process, in particular in #11665 , #11604, #11660 where we discuss the process.

Describe the solution you'd like
Add a proper JSON file describing such workflow into https://github.com/dmwm/WMCore/tree/master/test/data/ReqMgr/requests area which is used by inject script

Describe alternatives you've considered
Currently I use reduced version of TaskChain_MC.json from https://github.com/dmwm/WMCore/tree/master/test/data/ReqMgr/requests area where I reduce number of events, but it still requires full staging of the data, etc.

Additional context
Simplify debugging process of WMAgent components:

• we need to have ability to send simple, fake workflows
• we should be able to capture all logs from it
• we should capture all pkl and other intermediate files from such workflow in final job tarball.

FYI: @amaltaro , @todor-ivanov , @khurtado , @klannon