Generated OpenAPI has version 3.0.1 even though internally we use 3.1

[lukashornych]

Generated OpenAPI YAML/JSON has version 3.0.1 even though we use 3.1 for building io.evitadb.externalApi.rest.api.builder.RestBuildingContext#buildOpenApi. We also use 3.1 for serializing into YAML/JSON io.evitadb.externalApi.rest.api.resolver.endpoint.OpenApiSpecificationHandler.

There is no mention of 3.0.1 in the code. We need to either switch to 3.0.1 (maybe more desirable, not many tools support 3.1 apparently), or fix the correct version propagation into final documents.