[FR] Auto-retry FCM requests that failed due to an internal error (messaging/internal-error)

**Is your feature request related to a problem? Please describe.**
Our Sentry has captured about 20,000 messaging/internal-error errors. This means that due to some internal FCM error, we haven't sent 20,000 push notifications to our users.

**Describe the solution you'd like**
FCM documentation recommends retrying such requests. https://firebase.google.com/docs/cloud-messaging/send-message#admin.

Currently, the library retries 503 requests but not 500 (messaging/internal-error returns 500) https://github.com/firebase/firebase-admin-node/blob/b5c4f5ae551249b64632baf2ece7b5c594a1965f/src/utils/api-request.ts#L202

It would be nice to change the default retry configuration or allow library users to use their own retry configs. It seems the solution is already implemented in https://github.com/firebase/firebase-admin-node/pull/1739 but stuck in review phase for 2 years.

**Describe alternatives you've considered**
I considered writing a custom wrapper around the FCM error, but it appears that FCM doesn't expose the Retry-After header, making it unclear how long the wrapper should wait before making another request.

Additionally, copying and pasting the same wrapper in each project that uses FCM is a very frustrating experience

Start with src/utils/api-request.ts at the retry handling referenced in the issue, then review Firebase Cloud Messaging's retry guidance and pull request #1739. The change should cover messaging/internal-error responses and either update the default retry configuration or allow custom retry configurations.

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