Add default environmental variables

[mdesoto]

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It would be grand to have access to additional context information about the environment or instance exposed as environmental variables. To date, as far as I'm aware, the only one available is PORT. Google Cloud Run provides a few: K_SERVICE, K_REVISION, K_CONFIGURATION, PORT among others. And with App Runner, in the case of code deployed from source, having the hash of the commit would be tremendous.