SchemaRepository Injection into OpenAPIContract

#### Describe the feature

This stems from a concern that the provided interfaces prevent reuse of what should be immutable objects in memory. For context, to load up a `SchemaRepository`'s lookup table, we need to read in our schema files and then run them through a `dereference()`. The `OpenAPIContract` class does that alongside some validation in its `from()` function, which is really nice.

To explain the problem, now suppose that I have multiple open api files and thus need multiple OpenAPIContracts that produce routers that are eventually attached as subrouters for the rest server. Each OpenAPIContract will have its own SchemaRepository. Also consider that someone may want a fully hydrated `SchemaRepository` that I want to expose to a swagger ui or arbitrary http clients (I did that with a handler on some schema route that does the lookup/resolve for the schema and returns it). Every single OpenAPIContract and the separate SchemaRepository for exposing to clients will have duplicate/immutable schemas in memory.

The feature would be to genericize the validation/repo filling (which is filled by calling dereference() on the repo) logic in `OpenAPIContract::from`, probably moved into the vertx-json-schema library. Then allow a SchemaRepository to be provided to `OpenAPIContract::from`. That would allow the hydration of a SchemaRepository and then for it to be reused everywhere it is needed.

#### Use cases

The big use case is the reuse of SchemaRepository's for OpenAPIContracts and also the generalization of a very useful hydration feature for loading schemas into a SchemaRepository. OpenAPIContract is not the only class that can make use of that validation/repo filling logic. The only useful logic I've seen for filling a SchemaRepository's internal lookup map is in OpenAPIContract, but that's not something that should be specific to the openapi library.

Code reuse and saving on memory usage and startup time are the real benefits. In my eyes I would say that this is necessary polish.

#### Contribution

Who should implement this feature ? are you volunteering for implementing this feature or
do you know that is able and willing implement this feature ?