Added selector generation to Job's
strategy.Validate, right before validation.
Can't do in defaulting since UID is not known.

Added a validation to Job to ensure that the generated
labels and selector are correct when generation was requested.
This happens right after generation, but validation is in a better
place to return an error.

Adds "manualSelector" field to batch/v1 Job to control selector generation.
Adds same field to extensions/__internal.  Conversion between those two
is automatic.

Adds "autoSelector" field to extensions/v1beta1 Job.  Used for storing batch/v1 Jobs
    - Default for v1 is to do generation.
    - Default for v1beta1 is to not do it.
    - In both cases, unset == false == do the default thing.

Release notes:
Added batch/v1 group, which contains just Job, and which is the next
version of extensions/v1beta1 Job.

The changes from the previous version are:
- Users no longer need to ensure labels on their pod template are unique to the enclosing
  job (but may add labels as needed for categorization).
- In v1beta1, job.spec.selector was defaulted from pod labels, with the user responsible for uniqueness.
  In v1, a unique label is generated and added to the pod template, and used as the selector (other
  labels added by user stay on pod template, but need not be used by selector).
- a new field called "manualSelector" field exists to control whether the new behavior is used,
  versus a more error-prone but more flexible "manual" (not generated) seletor.  Most users
  will not need to use this field and should leave it unset.

Users who are creating extensions.Job go objects and then posting them using the go client
will see a change in the default behavior.  They need to either stop providing a selector (relying on
selector generation) or else specify "spec.manualSelector" until they are ready to do the former.

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Make #19601 backward compatible.

Fixes #20047

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Deployment: preserve availability when maxUnavailability is not 100%

Fix the nil pointer dereference when counting RS replicas

Fix the nil pointer dereference in addHashKeyToRSAndPods

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