docs: endorse secrets operators, caution against plugins (#21629)

[crenshaw-dev]

Closes #21629

[bunnyshell]

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[todaywasawesome]

I think this is solid as is. I suggested maybe adding the secret csi driver. We could potentially work in this talk about different approaches to managing secrets https://www.youtube.com/watch?v=FVaaqP7_AJg&t=1s - but it doesn't directly address the issues with hydration secrets management so I don't mind skipping. I actually think we need an updated talk on this.

[leoluz]

Tks for the doc. My comments are non blockers but suggestions.