Create new function app infrastructure

[JimCircadian]

• [x] Confirm if event target / subscription has to be in same RG as the event grid sources
• [x] Create base infrastructure
  • [x] Resource group name for function app
  • [x] Storage container for function app
  • [x] Storage container for processing configurations
  • [x] App service plan and application deployment
• [x] Create subscription to events from the ETL layer
  • [x] Subscription to the storage system provider for the input data storage
  • [x] Subscription to the new custom topic in the ETL layer for processing

[JimCircadian]

Manually created new EventProcessingTrigger for event grid triggers. Will test manual creation of subscription in the ETL layer and see if it's able to target this function

[JimCircadian]

Confirmed the subscriptions are created in this resource group but the system topics are "generated" in the case of storage account sources, which makes perfect sense, against the event grid sources in the other resource groups. The ETL processing (which will submit from the function app, probably) will provide a custom topic decoupling the internal triggering of events from the subscriptions. Therefore we can start straight away working with a subscription against the input storage container for blob / directory creation and work on that as a test case.

[JimCircadian]

The azurerm_eventgrid_system_topic_event_subscription cannot cross the resource groups to focus on the precreated system topic in the ETL layer. Therefore we need to create either a domain topic or an output service bus we can hook into

For the moment I've create a manual sub as this is taking a bit long and I need to test it. Will raise an issue to replace the above, which is currently commented out.