[release-1.23] 1.23.1 Release Notes

[mikemorris]

Manual pre-cherrypick of #15659 with feedback from #15659 (review) applied.

[istio-policy-bot]

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Courtesy of your friendly welcome wagon.

[dhawton]

Update release date prior to merge

[dhawton]

/retest

[dhawton]

/retest

flake