Schema Registry updates from Arch Board feedback

[JoshLove-msft]

Schema Registry

• Rename endpoint to fullyQualifiedNamespace in constructor (discuss with feature crew to decide on name)
• Add read-only FullyQualifiedNamespace property
• Add back Response for all methods (for async methods change from ValueTask to Task<Response>) and remove caching
• Investigate using BinaryData instead of string as the type for the Content parameter and property type in SchemaRegistrySchema (this would apply to at least Java, and possibly JS/Python)
• Rename content parameter to schemaDefinition
• Once GA service version is available, add it to ServiceVersion enum and remove the preview, and 2017 ones
• Rename SerializationType to SchemaFormat (property could be either Format or SchemaFormat - since we are already in the SchemaProperties)
• Investigate perf/API implications of adding a new SchemaId type #24037

Avro Serializer

• Investigate adding Serialize overload that take a SchemaId #24036
• Implement an LRU cache with 128 max entries - this does not need to be configurable for GA.
• Make the groupName parameter optional in the constructor (discussed this offline with Ted)

Docs

• Come up with guidance around the recommended use of AutoRegisterSchema and make sure it aligns with our default value.
• Go through Ted's feedback on the .NET README (and give feedback where it is relevant for other languages)