This adds the possibility to save SmallRye OpenAPI generated API document by setting the new `quarkus.smallrye-openapi.store-schema-directory`. This needs to be mentioned in the release notes.

• Pointer to the community guide(s): https://quarkus.io/guides/openapi-swaggerui#quarkus-smallrye-openapi_quarkus.smallrye-openapi.store-schema-directory
• Quickstart pointer: Same as above
• Known issues / limitations: Nothing I am aware of.
• Test coverage analysis for upstream testsuite: Not sure about this, but the test is here: https://github.com/quarkusio/quarkus/blob/master/extensions/smallrye-openapi/deployment/src/test/java/io/quarkus/smallrye/openapi/test/jaxrs/OpenApiStoreSchemaTestCase.java