feat: Cloud Functions Examples (User Provisioner)

[lanlooker]

• Rewrite README.me, include demo and environmental variable setup in Cloud Functions UI as gifs
• Refactor main.py and test with 4 cases:

1. An email of a new user: {"email": "me@gmail.com"} passed
2. An email of an existing user: {"email": "me@gmail.com"} passed
3. Wrong input: Typo in key "email" --> {"emails": "me@gmail.com"} passed (throwing an exception) 
4. Wrong input: Value of key "email" being an empty string passed (throwing an exception) 

• Fixing b/199953683, previous PR: docs(python): Google Cloud Function python SDK example #543
• Internal screencast: https://screencast.googleplex.com/cast/NDg1NDU2NjczNjYyNTY2NHw2MWRiNDk1Yi00YQ

Tagging @josephaxisa since you reviewed the previous PR. Thank you for taking a look

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[josephaxisa]

looks good to me. I left some suggestions :)

[josephaxisa]

nit: this can be changed to

Suggested change

	if user_id is not None:
	sdk.send_user_credentials_email_password_reset(user_id=user_id)
	return 'A user with this email: {email} already existed; Password reset sent'.format(email=email)
	elif user_id is None:
	create_users(email=email)
	return 'New user created; Setup/Welcome email sent to {email}'.format(email=email)
	if user_id:
	sdk.send_user_credentials_email_password_reset(user_id=user_id)
	return 'A user with this email: {email} already existed; Password reset sent'.format(email=email)
	else:
	create_users(email=email)
	return 'New user created; Setup/Welcome email sent to {email}'.format(email=email)

[josephaxisa]

LGTM. Looks like you need to accept the CLA though

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