Add Custom Time support in Firebase Cloud Storage Metadata

[nathanfallet]

Feature proposal

• Firebase Component: Storage (Auth, Core, Database, Firestore, Messaging, Storage, etc)

Add a way to set/get Custom Time Metadata in Firebase Cloud Storage

[paulb777]

Reopening. The SDK implementation looks correct in #9576, but it looks like the backend doesn't support the feature.

[nathanfallet]

@paulb777 Do you know if there is anything new on the backend? Or maybe I can help?

[paulb777]

@nathanfallet Sorry, I don't think anything on the backend has changed and its code is not open.