Support OpenAPI 3.1.x

[Indekkusu545]

Problem description

Currently APIM supports OpenAPI 3.1.x, but when using apim-cli to import OpenAPI 3.1.x, an error [APISpecificationFactory] DEBUG: Can't handle API specification with class: com.axway.apim.api.specification.OAS3xSpecification will be reported.

Feature request

Support OpenAPI 3.1.x

[florianstoll]

Support for OpenAPI 3.1.x is needed via apim-cli to deploy current APIs into API Manager. API Manager already has support for OpenAPI 3.1.x.

[florianstoll]

@rathnapandi Could you please review MR #546?