Automatic merge from submit-queue (batch tested with PRs 39486, 37288, 39477, 39455, 39542)

Allow missing keys in templates by default

Switch to allowing missing keys in jsonpath templates by default.

Add support for allowing/disallowing missing keys in go templates
(default=allow).

Add --allow-missing-template-keys flag to control this behavior (default=true /
allow missing keys).

Fixes #37991

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