Support for detecting changes in webhooks

[caristu]

It would be nice to support API changes in webhooks defined with OpenAPI 3.1, in particular:

1. Detect if a webhook is removed
2. Detect changes in the webhook payload

Unfortunately it looks like now this is not possible.

This can be reproduced by doing:

    String oldSpec = Paths.get("webhook1.yml").toUri().toString();
    String newSpec = Paths.get("webhook2.yml").toUri().toString();

    ChangedOpenApi diff = OpenApiCompare.fromLocations(oldSpec, newSpec);

The content of boths specs are attached here (as .txt but they are .yml specs)

webhook1.txt

webhook2.txt

Note that no differences are found in this case