Lock Down Values in Pulumi ESC with fn::final

Pulumi ESC (Environments, Secrets, and Configuration) allows you to compose environments by importing configuration and secrets from other environments, but this also means a child environment can silently override a value set by a parent. When that value is a security policy or a compliance setting, an accidental override can cause real problems. With the new fn::final built-in function, you can mark values as final, preventing child environments from overriding them.