[EG] maps required/optional

[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=2d377c8b33be4f44a989ab3fd4cd95fa
Python	azure-eventgrid	https://apiview.dev/Assemblies/Review/c554ddbabc6e40348998b1656e0ff585?revisionId=142921025afc40f5962c0e200245ef3c
Swagger	Microsoft.EventGrid	https://apiview.dev/Assemblies/Review/8dab2e78889f4bf4a935473df37e62bf?revisionId=dcf77e0efd5046e591f09071bc38f4ae
TypeSpec	Azure.Messaging.EventGrid.SystemEvents	https://apiview.dev/Assemblies/Review/bf48b2982ff74cd796f5900a221af2d5?revisionId=4eb7ebc4209d4a63b13abb3a7164c544