Update documentation

[SzymanskiBartlomiej]

This pull request includes significant updates to the OpenAPI documentation for the backend, specifically focusing on enhancing the simulation results and estimator metadata retrieval endpoints. The changes include adding new query parameters for pagination, updating response descriptions, and introducing new schemas for better structuring the data.

Enhancements to simulation results retrieval:

• docs/backend/openapi.yaml: Updated the description for the /results endpoint to include details about the new page_number and page_numbers query parameters, which allow for paginated retrieval of results.
• docs/backend/openapi.yaml: Added page_number and page_numbers as optional query parameters in the /results endpoint to support paginated results.
• docs/backend/openapi.yaml: Introduced new response objects to include pagination information in the /results endpoint.

Enhancements to estimator metadata retrieval:

• docs/backend/openapi.yaml: Updated the summary and response description for the /estimators endpoint to reflect the retrieval of estimator metadata instead of just names.
• docs/backend/openapi.yaml: Added detailed properties for the estimators_metadata response, including page metadata.

Schema updates:

• docs/backend/openapi.yaml: Added a new Page schema to represent page objects in the API responses.
• docs/backend/openapi.yaml: Updated the Estimator schema to reference the new Page schema for better data structuring.

Additional changes:

• docs/backend/persistency.md: Updated the class diagram to include new fields file_name, page_name, and page_dimension in the PageModel class.