Set rollingUpdate to null when updateStrategy is Recreate

[minhdanh]

What this PR does / why we need it:

This PR adds "rollingUpdate": null to updateStrategy of the statefulsets when the type of updateStrategy is Recreate.
This is needed in case someone initially uses the default strategy, which is RollingUpdate, but then decides to change it to Recreate for some reason (such as pv mounting issue on some platforms).
In that case they will not be able to update the strategy with such below error:

Error: StatefulSet.apps "postgres" is invalid: spec.updateStrategy: Invalid value: apps.StatefulSetUpdateStrategy{Type:"Recreate", RollingUpdate:(*apps.RollingUpdateStatefulSetStrategy)(nil)}: must be 'RollingUpdate' or 'OnDelete' && StatefulSet.apps "postgres" is invalid: spec.updateStrategy: Invalid value: apps.StatefulSetUpdateStrategy{Type:"Recreate", RollingUpdate:(*apps.RollingUpdateStatefulSetStrategy)(nil)}: must be 'RollingUpdate' or 'OnDelete'

By adding "rollingUpdate": null, this will solve that issue.

See also: kubernetes/kubernetes#24198

Special notes for your reviewer:

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• DCO signed
• Chart Version bumped
• Variables are documented in the README.md

[k8s-ci-robot]

Hi @minhdanh. Thanks for your PR.

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[minhdanh]

/assign @desaintmartin

[juan131]

Thanks so much for this fix!

[juan131]

/ok-to-test
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: juan131, minhdanh

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