Update the migration guide to document that processor checkpoints from legacy versions are not applied

[jsquire]

Summary

In order to align with the goal of supporting cross-language checkpoints and a more efficient means of tracking partition ownership, the EventProcessorClient does not consider or apply checkpoints created with the legacy Microsoft.Azure.EventHubs.Processor family of types. This is a potential area of confusion and should be highlighted for consideration within the migration guide.

Scope of Work

• Enhance the migration guide to call out that checkpoints and ownership data are not carried forward from the legacy Event Hubs processor types.

• Consider adding instructions to manually copy/apply the data between formats or a tool to perform the migration of checkpoint data from the legacy format.

Success Criteria

• The migration guide documents the behavior of the EventProcessorClient regarding legacy checkpoints and sets clear expectations for developers migrating to the new library.

Related Items

• Create a utility to demonstrate migration of legacy checkpoints for use with the EventProcessorClient (#11373)