[chart csi-isilon] add ability to set priorityclassname to controller and node

[SebPlv]

Is this a new chart?

No

What this PR does / why we need it:

This PR adds the ability to set a PriorityClassName to de Controller deployment and the Node Daemonset of csi-isilon.

Which issue(s) is this PR associated with:

None

Special notes for your reviewer:

Checklist:

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

• Chart Version bumped
• Variables are documented in the chart README.md
• Title of the PR starts with the chart name (e.g. [charts_dir/mychartname]) if applicable

[coulof]

Thanks for your contribution @SebPlv !

I understand you need the priorityClassName but I'm not sure this is widely adopted.

While waiting for the engineering review, I can suggest that you use Kustomize to patch the helm chart.

You can find an example in context of this patch here : https://gist.github.com/coulof/aacc92e4a95cff85d5c5693aedb7c980

And more details on why it can be a good solution here : https://storage-chaos.io/kustomize-and-helm-better-together.html