Initially it would validate only shell scripts.

Tasks:

1. add a lint target to the Makefile, like this: https://github.com/maistra/istio-operator/blob/maistra-2.3/Makefile#L274-L281
2. add a job to our CI to automatically run this job for PR's in 2.2. and 2.3 branch, similar to this one: https://github.com/maistra/test-infra/pull/240