Allow command override in halyard jobs

[jjtowers]

What
Add the ability to override the command run on each Halyard job (install and cleanup).

Justification
When this chart is used while, for example, having a service mesh configuration on such as Istio, jobs require a custom command to be run.

(In this specific scenario, service mesh keeps running while the jobs are already finished, but overall pod status is Running instead of completed)