[Azure Mgmt Generator] Disable some meaningless upstream diagnostic warnings #54717
Description
Our upstream has some warning diagnostics, such as @azure-tools/typespec-client-generator-core/unsupported-generic-decorator-arg-type from TCGC, @typespec/http-client-csharp/unsupported-patch-convenience-method from Azure Generator.
They do not really cause a thing in mgmt plane's generated code, therefore they are just spamming the output right now.
We should find a way to filter those diagnostics out.