BUG: v3 Catch KeyError and Raise BadRequestError for Invalid phone_info

Description

With the change to the API for a similar issue in v2 on #1525, we now return an error on POST sms with an invalid prefix. v3 however defers validation downstream and so we still get a long stacktrace. This error should be handled better for v3.

[ ] Ticket is understood, and QA has been contacted (if the ticket has a QA label).

Steps to Reproduce

send a POST v3/sms request with the following payload

{
"template_id": "{{sms-template-id}}",
"phone_number": "+80888888888"
}

Observe that a 202 and a notification id is returned by the route, but GET v2/notifications/{notification-id} stays stuck at creating
Observe the following logs

Workaround

Is there something we can do to work around this issue in the meantime? None

Impact/Urgency

Poor experience, should be resolved before we release v3.

Expected Behavior

This is an engineering decision point since we are deferring certain validations. But this should not result in a long stacktrace in the logs and a status of 'creating'.

QA Considerations

[ ] add test to regression for this use case

department-of-veterans-affairs / notification-api