Fixed some invalid examples
Fixed some invalid examples

It is understood that most examples showcased in the OAS spec are snippets, not entire OAS documents. However some of those snippets would not be valid even if included in entire OAS documents. This PR is an attempt to fix some of those examples.

**List of changes**:
- added a `GeneralError` schema inside the `Components Object Example`
- split the `Example Object Example` into multiple examples
OAI/OpenAPI-Specification,OAI/OpenAPI-Specification,OAI/OpenAPI-Specification