Ephemeral-storage documentation update for plugin requirements

[msfrucht]

Please add a summary of your change

I hit an interesting issue with ephemeral-storage as of late with OCP 4.16.

OCP and similar Kubernetes variations add ephemeral-storage to kubernetes resourceAllocations as options besides CPU and memory. Ignored in most Kubernetes clusters.

Previous versions of OCP did not notice ephemeral-storage usage from plugins as they are finished setting up in the container at startup time. As a result, ephemeral-storage could be set as low as limits of 25Mi or less.

With new installs, ephemeral-storage violations on installation. And eventually tracked down the issue to the /plugins directory.

These estimates are based on current object storage providers. It is entirely possible some plugins will exceed the estimated 100MB per plugin, but this seems to a comfortable estimate at current for some of the more common plugins.

From our own testing of Velero 1.14.1 object storage plugins and a couple of item transformation plugins.

sh-5.1$ du -h plugins/*
63M     plugins/kubevirt-velero-plugin <--- kubevirt item transformation plugin
83M     plugins/velero-plugin-for-aws <--- Amazon AWS object storage and snapshotter plugin
62M     plugins/velero-plugin-for-gcp <--- Google Cloud object storage and snapshotter plugin
52M     plugins/velero-plugin-for-microsoft-azure <-- Microsoft Azure storage and snapshotter plugin
91M     plugins/velero-plugins <--- OpenShift item transformation plugin
sh-5.1$ du -h  plugins 
348M    plugins

Does your change fix a particular issue?

Documentation for resolving ephemeral-storage plugin requirements seen in OpenShift 4.16 and any other Kubernetes cluster or environment that monitors and restricts ephemeral-storage usage.

Fixes #(issue)

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• Accepted the DCO. Commits without the DCO will delay acceptance.
• Created a changelog file (make new-changelog) or comment /kind changelog-not-required on this PR.
• Updated the corresponding documentation in site/content/docs/main.

/kind changelog-not-required

[msfrucht]

/kind changelog-not-required

[kaovilai]

please force push and/or reopen pr to trigger changelog check due to issue.

[codecov]

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