Event Hub components should expose initialOffset in manifest to control starting position (like Kafka)

[oising]

Describe the feature

When an PubSub or Binding component starts up with an empty/new checkpoint store, it starts at the latest position in the backing store. There should be an option to allow starting at the earliest.

Kafka supports this with initialOffset

See https://github.com/Azure/azure-event-hubs-go/blob/3dc3aeb6144e5d79a70d32f023f9d5990f81569d/persist/checkpoint.go#L29 in the azure SDK go SDK for the mechanism to support this.

Release Note

RELEASE NOTE:

[github-actions]

This issue has been automatically marked as stale because it has not had activity in the last 30 days. It will be closed in the next 7 days unless it is tagged (pinned, good first issue, help wanted or triaged/resolved) or other activity occurs. Thank you for your contributions.

[oising]

Bump.