Migrate backend openapi document validation to apicurio-data-models library

Created from https://issues.redhat.com/browse/ENTESB-11443

Currently when importing an openapi document we have a mismatch between how the document is validated by the embedded apicurio editor and the Syndesis backend, leading to different warnings/errors shown to the user. We should consider using the same validation engine as apicurio so that at least basic document validation is consistent.

It's possible however we may need to continue to have additional warnings if there's features we can't support in an API provider integration.