Add beforeSendEmail and beforeSendSms blocking functions samples

[macastelaz]

Supplement samples in Node and Python to include examples of beforeSendEmail and beforeSendSms

[gemini-code-assist]

Code Review

This pull request introduces new Firebase Auth Blocking functions for both Node.js and Python quickstarts. It adds beforeEmailSent and beforeSmsSent triggers to block email sending to non-acme.com domains and SMS sending to non-US phone numbers. The review comments suggest minor readability improvements in the Node.js functions by explicitly checking for the existence of user.email and user.phoneNumber before calling string methods, even though optional chaining provides functional safety.

[gemini-code-assist]

Using optional chaining with includes on a potentially undefined email property is safe, but for better readability and explicit null checking, consider checking if the email exists before calling includes.

Suggested change

	if (!user?.email?.includes("@acme.com")) {
	if (user?.email && !user.email.includes("@acme.com")) {

[gemini-code-assist]

Similar to the email check, explicitly validating the existence of phoneNumber before calling startsWith improves code clarity.

Suggested change

	if (!user?.phoneNumber?.startsWith("+1")) {
	if (user?.phoneNumber && !user.phoneNumber.startsWith("+1")) {