httpTimeout option in initializeApp

**Is your feature request related to a problem? Please describe.**
In the Python implementation of firebase_admin, there is an option on [initialize_app](https://firebase.google.com/docs/reference/admin/python/firebase_admin#initialize_app) that allows the httpTimeout to be set manually. There is no such implementation in NodeJS.

**Describe the solution you'd like**
The desired solution is to have the same functionality of httpTimeout in the Python firebase_admin, implemented for the NodeJS firebase-admin.

**Additional context**
Using firebase-admin version 9.4.2

Start at the Node.js firebase-admin initializeApp entry point and compare its options with the linked Python initialize_app reference. Done means Node.js callers can set httpTimeout through initializeApp and the configured timeout is honored; verify the behavior with the relevant initializeApp tests.

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