docs: update README and example.env to include Twilio Verify credentials

[ab-elhaddad]

What kind of change does this PR introduce?

Update README and example.env to include the Twilio Verify credentials

What is the current behavior?

Only Twilio Messaging credentials is mentioned (mentioned as twilio), although the auth server supports Twilio Verify

What is the new behavior?

Add the Twilio Verify credentials

Additional context

As you can see here and here twilio_verify is a valid SMS_PROVIDER value. And here the credentials needed is defined.