Improve error message when the service doesn't have a protocol trait applied #2452
Description
Currently, if you don't specify a protocol trait in your service, you get an error like this:
Projection test-service failed: software.amazon.smithy.codegen.core.CodegenException: No matching protocol — service offers: []. We offer: [aws.protocols#restJson1, aws.protocols#restXml, aws.protocols#awsJson1_0, aws.protocols#awsJson1_1]We should clarify that you should probably put one of those traits in your model. And also improve formatting (add some line breaks).