[EG] SignalR Required/Optionality

[openapi-pipeline-app[bot]]

Next Steps to Merge

Next steps that must be taken to merge this PR:

• ❌ This is the public specs repo main branch which is not intended for iterative development.
  You must acknowledge that you understand that after this PR is merged, you won't be able to stop your changes from being published to Azure customers.
  If this is what you intend, add PublishToCustomers label to your PR.
  Otherwise, retarget this PR onto a feature branch, i.e. with prefix release- (see aka.ms/azsdk/api-versions#release--branches).
• ❌ This PR has at least one breaking change (label: BreakingChangeReviewRequired).
  To unblock this PR, follow the process at aka.ms/brch.
• ❌ The required check named Swagger BreakingChange has failed. To unblock this PR, follow the process at aka.ms/brch.

[openapi-pipeline-app[bot]]

Generated ApiView

Language	Package Name	ApiView Link
.Net	Azure.Messaging.EventGrid.SystemEvents	https://apiview.dev/Assemblies/Review/3e102a891e5445af8be8cde833dbb702?revisionId=868f3684efa44c9e8c1fba782c8041f1
Python	azure-eventgrid	https://apiview.dev/Assemblies/Review/c554ddbabc6e40348998b1656e0ff585?revisionId=983c1a05ca0044d9954502423653581f
TypeSpec	Azure.Messaging.EventGrid.SystemEvents	https://apiview.dev/Assemblies/Review/bf48b2982ff74cd796f5900a221af2d5?revisionId=c998d58abaa14c3f9219177b9d91a2a8
Swagger	Microsoft.EventGrid	https://apiview.dev/Assemblies/Review/8dab2e78889f4bf4a935473df37e62bf?revisionId=a90e5fa919204697b9e34b67664280a9