Support configuring upstream zone sizes in VS/VSR

[LorcanMcVeigh]

Proposed changes

Extended upstream zone size support to nginx plus and vs/vsr

Checklist

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto master
• I will ensure my PR is targeting the master branch and pulling from my branch from my own fork

[Dean-Coakley]

1. I think we need to do some validation in https://github.com/nginxinc/kubernetes-ingress/blob/master/pkg/apis/configuration/validation/validation.go#L282 ? I suggest writing a reuseable func validateSize to ensure a valid [size] was specified.

2. An example and docs should be included in: https://github.com/nginxinc/kubernetes-ingress/blob/master/docs/virtualserver-and-virtualserverroute.md#upstream

[pleshakov]

@LorcanMcVeigh thanks for the PR. Please see my comments.

Thanks for the comments @Dean-Coakley However, they are not applicable because extending the VS/VSR resources upstream field is not part of this task. However, the configmap key upstream-zone-size must affect the generated config for VS/VSR. At the same time, please update the description of the upstream-zone-size entry in the configmap table for the case of NGINX Plus.

[pleshakov]

@LorcanMcVeigh thanks for the update. Please see an additional suggestion.
Also, the comment about the documentation wasn't addressed. We need to update the documentation to cover NGINX Plus.

[pleshakov]

looks better! Please see the suggestions for the added parts.

[Rulox]

lgtm, just a small comment, let me know if it makes sense.

[pleshakov]

Please see additional comments

[pleshakov]

thanks @LorcanMcVeigh looks like we're almost there. Please see a few suggestions

[pleshakov]

👍