When injecting a Cronjob with no
`spec.jobTemplate.spec.template.metadata` we were getting the following
error:
```
Error transforming resources: jsonpatch add operation does not apply:
doc is missing path:
"/spec/jobTemplate/spec/template/metadata/annotations"
```
This only happens to Cronjobs because other workloads force having at
least a label there that is used in `spec.selector` (at least as of v1
workloads).
With this fix, if no metadata is detected, then we add it in the json patch when
injecting, prior to adding the injection annotation.
I've added a couple of new unit tests, one that verifies that this
doesn't remove metadata contents in Cronjobs that do have that metadata,
and another one that tests injection in Cronjobs that don't have
metadata (which I verified it failed prior to this fix).
Alejandro Pedraza