[REQ] Handle list of String special case in webclient generator

Created by: dlicois

Is your feature request related to a problem? Please describe.

When describing an operation that returns an array of string, the openapi-generator for java-webclient generates an api returning a Flux<String>.

However Spring's Webclient handles serialization of JSON array of strings in a special way : spring-projects/spring-framework#22662

This means expecting a Flux<String> when a server return an array of String is a mistake.

Please see sample Gradle project https://github.com/dlicois/webclient-liststring, it contains a test class (WebClientListStringTest.java) to better explain the behaviour. The openapi.yaml describes an operation returning an array of string, openapi-generator generates a DefaultApi.java class returning a Flux<String>. When the webclient receive the answer ["one","two", "three"], it publishes a single String of value ["one","two", "three"]. I would have expected three Strings.

This makes the generated api unusable for this case, requiring to parse the response a second time to handle it.

Describe the solution you'd like

Recommended solution by Spring developers (see spring-projects/spring-framework#22662 and https://docs.spring.io/spring/docs/current/spring-framework-reference/web-reactive.html#webflux-codecs-jackson) is to use a Mono<List> for string arrays.

This would mean making a special case for operations described as arrays of string to generate a Mono<List> instead of Flux.