[v3-1-test] Update pmc verification docs (#61271)

[bugraoz93]

backport: #61271

• Update Helm Chart release instructions for PMC Checks

• Update KEY download instructions for PMC Checks

• Update dev/README_RELEASE_HELM_CHART.md (cherry picked from commit c74b24a)

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[bugraoz93]

This should be backported before #61291 to keep things easier. Just info

[bugraoz93]

On a second thought it doesn't really matter :D

[bugraoz93]

Added WIP to prevent further merges so we can make it work fully
cc:@jscheffl

[bugraoz93]

Jed fixed this part will merge this and backport from that should fix the part already in main. Not merging this also makes backport harder to choose