[Analyzer] Ensure Minimal API Endpoint Returns On All Paths

Given that a Minimal API endpoint uses the `Delegate` or `RequestDelegate` type, it is technically valid that not all paths have return values. While this is valid `C#` code, it likely is not the intent of the developer. Here's an example of a compilable endpoint that results in an unintended result.


The bug is subtle and could likely cause frustration.

## Solution

Create an analyzer that determines if all paths in an endpoint result in a return value or exception being thrown.