Add `Origin` and `Access-Control-Request-Method` to Pre-flight request header

### Is your feature request related to a problem? Please describe.
When [server app](https://github.com/Azure/azure-webpubsub/blob/main/samples/javascript/chatapp/server.js) is deployed on EashAuth enabled Azure Web App, a pre-flight request of CloudEvent from Azure Web PubSub to the event handler on the Web App is always denied (401 returns).

### Describe the solution you'd like
Currently, the request headers as pre-flight from Azure Web PubSub are followings.
- host
- webhook-request-origin
- x-forwarded-for
- x-forwarded-proto
- accept-encoding

But as long as I investigated, EasyAuth can accept the request as CORS pre-flight only when both headers of `Origin` and `Access-Control-Request-Method` are included in the request.

### Additional context
Actually, I'm not sure which side, EashAuth or Azure Web PubSub, should be fixed.
Possibly they both follow each specification.