Feature request: Add support for manipulating schemas generation via ISchemaFilter

**Describe the issue**
It would be nice to allow to implement custom logic to manipulate the generation of operations and schemas, similarly to what Swashbuckle provides: [Extend Generator with Operation, Schema & Document Filters](https://github.com/domaindrivendev/Swashbuckle.AspNetCore#extend-generator-with-operation-schema--document-filters)

**Example use cases**
* Extend the schema when not using DataAnnotations but a different form of validation (e.g. the popular FluentValidation)
* Change the handling of request or response types (like enums) via ISchemaFilter

This feature is a successor of feature request #376 after the support of IDocumentFilter where implemented.

Start by reviewing the prior request in issue #376 and the linked Swashbuckle documentation on operation, schema, and document filters. Define the expected ISchemaFilter behavior for custom schema and type handling, then identify the relevant generation tests and add coverage showing when the feature is complete.

Written by the indexing model from the issue text.