Clear Event Hub Device Watermarks when source event hub changed

[pallar-ms]

Description -
When customer changes their source of events (source event hub) the IoT Connector watermark should be reset and process all data available from the earliest available point in the event hub.

Changes -

• Append event hub name to the checkpoint blob path
• Delete checkpoints corresponding to an older source event hub
• Note - This change is applicable to the event hubs for both the app types (i.e. watermarks will be handled in the same fashion for input event hub or the normalization event hub, but they are independently maintained.)

Testing -

• Manual testing by running the Fhir.Ingest console app and verifying the various scenarios
  • Change event hub namespace
  • Change event hub within the same event hub namespace
  • Same event hub
• Added UTs for reset checkpoints

PENDING -
Once this change takes effect, the checkpoints in the older path will not be honored, which will trigger reprocessing of the data. To avoid this, we can copy over the older checkpoints to the new location. Dustin is helping gauge how many active Gen2 connectors we have and the size of data ingested, to assess the impact and take the call accordingly. Will not be closing this PR until then, but putting this out now for first pass of review.

[dustinburson]

🕐

[dustinburson]

Overall looks good. Added a few more suggestions.