Add API call examples for creating and editing Wikidata works and authors

This merge request closes issue T405635

This merge request adds a new api-call-examples.md file containing practical examples for using the Wikibase REST API to create and edit Wikidata items.

Key additions:

Example API call to create an author item with label, description, and key statements (instance of, sex or gender, occupation).

Example API call to create a work item with label, description, and relevant statements (instance of, form of creative work).

Example API call to add a new statement to an existing author item.

Example API call to modify an existing statement.

Included references to official Wikidata REST API documentation for further reading.

It provides a ready reference for developers to implement item creation and editing through the Wikibase REST API, which can be used in Paulina’s backend integration.