PVC and containers share the same ResourceRequirements struct. The Claims field
in it only makes sense when used in containers. When used in a PVC, the field
should have been rejected by validation. This was overlooked when introducing
it, so now persisted objects might have it set and/or people may have started
to rely on it being accepted even when it has no effect.
Therefore we cannot reject it in validation anymore, but we can still strip
it out on create or update.
Modify the behavior of the AnyVolumeDataSource alpha feature gate to enable
a new field, DataSourceRef, rather than modifying the behavior of the
existing DataSource field. This allows addition Volume Populators in a way
that doesn't risk breaking backwards compatibility, although it will
result in eventually deprecating the DataSource field.
Update the unit tests to include checks for incorrect APIGroup type in
PVC DataSource and change the name of the feature gate to be more clear:
s/VolumeDataSource/VolumePVCDataSource/
