vector _pod.tpl does not offer envFrom

[mdaniel]

We have an existing Secret that would be very handy for providing to vector just like we provide it to other workloads, but the current _pod.tpl only accepts .Values.env, wherein we have to unpack the keys using secretKeyRef

I wanted to bring that missing envFrom to your attention

[spencergilbert]

Ah - easy enough to add in, I feel like I remembered that being under the same env key 🤔

I'll look to add this in when I get a chance, otherwise happy to accept a contribution.