Add gerrit verifications for the out-of-tree dahdi-linux kernel module.
Put this in a separate file (not gerrit-verifications.yml), because:
* not only gerrit git repo gets cloned, but also linux.git, and caching
needs to be done properly for it
* so we can have one separate job per linux version that gets tested
Test v4.19 and v5.10 for now, as suggested in the issue.
Related: OS#5407
Depends: docker-playground Id72d19ad08681cd7cb3194de2226292f19e96df5
Change-Id: I65c7663a6b8045796536a727e4adf5554f16b2a9
