Implement monitoring for invalid rep addresses

[oddball-lindsay]

Background

We discovered in #93624 that there were 657 representatives with an invalid address, which resulted in their latitude and longitude being set to 0 and thus did not allow the representatives to be associated by users' search locations as expected.

The fix will be tackled in #94579, but it'd also be nice to set up monitoring so that we can be more aware if any other representatives have invalid addresses.

Tasks

• Set up Data Dog monitoring for when addresses are invalid
• Route notifications to #benefits-representation-management-notifications Slack channel

Acceptance Criteria

• The ARM team will be notified when representatives have invalid addresses.