[Core] Fix memory leak due to repetitive registration of FastAPI routes

[talsabagport]

Description

What - Fix memory leak due to repetitive registration of FastAPI routes

Why - Constant memory leak when registering FastAPI routes

How - Run app setup just once

Type of change

Please leave one option from the following and delete the rest:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• New Integration (non-breaking change which adds a new integration)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Non-breaking change (fix of existing functionality that will not change current behavior)
• Documentation (added/updated documentation)

All tests should be run against the port production environment(using a testing org).

Core testing checklist

• Integration able to create all default resources from scratch
• Resync finishes successfully
• Resync able to create entities
• Resync able to update entities
• Resync able to detect and delete entities
• Scheduled resync able to abort existing resync and start a new one
• Tested with at least 2 integrations from scratch
• Tested with Kafka and Polling event listeners
• Tested deletion of entities that don't pass the selector

[shalev007]