[Doc]Expand doc to emphasize that the name of the event hub and EntityPath must match

[karenzone]

Topic: https://www.elastic.co/guide/en/logstash/current/plugins-inputs-azure_event_hubs.html

Enhance azure_event_hubs documentation to emphasize that the name of the event hub defined in the advanced configuration must match the EntityPath value in the event_hub_connection if one is defined.

event_hubs => [
{ "event_hub_name1" => {
event_hub_connection => "Endpoint=/;SharedAccessKeyName=;SharedAccessKey=___
;EntityPath=event_hub_name1"
consumer_group => "logstash" # shared across all Event Hubs
}}
]
}

Ideas:

• Add a note to event_hub_connection option
• Add/expand code samples with callouts
• What else?

[robbavey]

@karenzone I think expanding the Advanced Configuration section makes sense - to call out how to define the event hub names, and also talk about how to configure the plugin to use multiple event hubs with the same name, with the use of storage containers.