EventHub configurations PATCH Method

**Is your feature request related to a problem? Please describe.**
Event hubs are created using the sdk with minimal configurations, the end users also has full fledged permissions to go and update via portal once created.

Current challenge is we also store initial configuration in a Database and reconcile the resource if some changes are done to it. With this the configurations done in portal are lost.

**Describe the solution you'd like**
PATCH method for the Event HUB update

**Describe alternatives you've considered**
Get the settings and apply delta sync to the resource.

Start by locating the Event Hubs REST API specification in the azure-rest-api-specs repository and read the issue discussion. Determine the existing update operations and the intended PATCH or delta-sync behavior, then define what resource settings must remain unchanged when portal modifications are reconciled.

Written by the indexing model from the issue text.