DCAwareRoundRobinPolicy: Raise an error for an unconfigured DC

Description

In the next major and as part of PYTHON-811, specifying a DC aware LBP without also specifying an explicit DC will result in an exception (or warning? The debate isn't clear yet). Make sure error messages for an unconfigured DC using a DC aware policy actually show the available DCs, and possibly a snippet for how to configure it in code.

Environment

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Pull Requests

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Assignee

Unassigned

Reporter

James Falcon

Fix versions

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Pull Request

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Sprint

Py P-MAJOR-NEXT

Priority

Major