Event hub Samples issue

[v-xuto]

Section link1,link2,link3,link4,link5,link6:

Reason:
ValueError: The eventhub name can not be None or empty.

Suggestion:
Add a comment to CONNECTION_STR # connection string contains EventHub name.
Or
Add parameter eventhub_name=EVENTHUB_NAME , uptate to:

consumer_client = EventHubConsumerClient.from_connection_string(
    conn_str=CONNECTION_STR,
    consumer_group='$Default',
    checkpoint_store=checkpoint_store,  # For load-balancing and checkpoint. Leave None for no load-balancing.
    eventhub_name=EVENTHUB_NAME
)

@jongio for notification.

[yunhaoling]

thanks @v-xuto , doc/sample fix PR merged: #16457