docs: added internal research on salt job callbacks
docs: added internal research on salt job callbacks

Open sourcing an internal research that was done by @jimmykarily.

Signed-off-by: Miquel Sabaté Solà <b4d70704b9e7df580cab34510621dbd0aacb2dfd@suse.com>

ereslibre/velum,irfanhabib/velum,irfanhabib/velum,vitoravelino/velum,irfanhabib/velum,ereslibre/velum,ereslibre/velum,kubic-project/velum,vitoravelino/velum,MaximilianMeister/velum,irfanhabib/velum,MaximilianMeister/velum,kubic-project/velum,vitoravelino/velum,MaximilianMeister/velum,ereslibre/velum,vitoravelino/velum,kubic-project/velum,kubic-project/velum,MaximilianMeister/velum