[BUG][SPRING] Hardcoded version of swagger-ui in Spring Boot generated code

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue? (N/A)
• Have you validated the input using an OpenAPI validator (N/A)
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?

Description

Spring Boot generated code hardcodes a version of Swagger-UI.

eg. in OpenAPI2SpringBoot.java

registry.addResourceHandler("/swagger-ui/**").addResourceLocations("classpath:/META-INF/resources/webjars/swagger-ui/3.14.2/");

• https://github.com/OpenAPITools/openapi-generator/blob/b5ae21b090797db0cba37a92de59e77e5562c7be/samples/server/petstore/springboot-reactive/src/main/java/org/openapitools/OpenAPI2SpringBoot.java#L53
• https://github.com/OpenAPITools/openapi-generator/blob/0fca90133ce097f987098e6121936c0ffcb210a8/modules/openapi-generator/src/main/resources/JavaSpring/libraries/spring-mvc/openapiUiConfiguration.mustache#L74
• https://github.com/OpenAPITools/openapi-generator/blob/b5ae21b090797db0cba37a92de59e77e5562c7be/modules/openapi-generator/src/main/resources/JavaSpring/libraries/spring-boot/openapi2SpringBoot.mustache#L68

This means if you use a different version of Swagger UI (current latest is 3.22.0) the UI is not present in the webapp, without any errors or indication of the problem.

openapi-generator version

Maven Plugin 3.3.4

OpenAPI declaration file content or url

Not related to any specific OpenAPI config.

Command line used for generation

<configOptions>
  <sourceFolder>src/gen/java/main</sourceFolder>
  <java8>true</java8>
  <reactive>true</reactive>
  <apiPackage>gen.api</apiPackage>
  <modelPackage>gen.model</modelPackage>
  <invokerPackage>gen.invoker</invokerPackage>
  <delegatePattern>true</delegatePattern>
</configOptions>

Steps to reproduce

• add a version of swagger-ui other than 3.14.2
• generate API
• /swagger-ui/index.html not found
• add version 3.14.2
• /swagger-ui/index.html available

Related issues/PRs

None

Suggest a fix

Make the Swagger-UI version configurable.

Start with modules/openapi-generator/src/main/resources/JavaSpring/libraries/spring-mvc/openapiUiConfiguration.mustache and openapi2SpringBoot.mustache, then compare the generated OpenAPI2SpringBoot.java shown in the report. Reproduce with a Swagger UI version other than 3.14.2 and inspect the generated /swagger-ui/ route. Done means the Swagger UI version is configurable and the route works with the configured dependency version.