[jobs-api] move custom validations out of api models
- remove cap from replica value from openapi spec (seems like an oversight)
- remove most custom pydantic validations and move them to both tjf/core/job.py and tjf/runtimes/k8s/jobs.py (depending on where they are most suitable for)
- refactor from_job ( some things there are legacy of the previous job comparision feature. Now job comparisons are done on the k8s side some of these things are no longer needed here )
Depends-on: jobs-cli!96
Bug: T389118
Signed-off-by: raymond-ndibe rndibe@wikimedia.org