[Micronaut] Parameter bean validation issues

On using the micronaut code generator, there were few issues with regards to how the bean validations were applied on the api interfaces generated

1. if a query parameter is declared as required, in the swagger file the generated API has 2 declarations of @NotNull
2. if a parameter(query or header) is declared as required: false, Micronaut requires an explicit @Nullable keyword
3. header parameters do not have bean validation implemented currently (e.x Pattern , Size, minLength etc)

Start at the Micronaut code generator entry point and locate the templates that produce API interfaces and parameter annotations. Compare generated query and header parameters with the Swagger requirements, then verify that required parameters have one validation annotation, optional parameters are explicitly nullable, and header constraints are emitted.