Add note on GKE metadata server Workload Identity (#10728)
Add note on GKE metadata server Workload Identity (#10728)

* Add note on GKE metadata server Workload Identity

cc: 7398febc3c9bc6db3b6a8f0cc1f2e6ead7a0bf78@potiuk

* fixup! move detailed notes on ADC to separate section

* fixup! remove trailing whitespace
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