OpenAPI models generation: switch to using Docker for the generator

[pavelnikonorov]

To streamline setup and minimise local dependency installations, the official Docker container for OpenAPI Generator CLI might be a more convenient alternative. This container includes all required dependencies, eliminating the need for a local Java installation and other setup steps. Available directly on Docker Hub, this solution can simplify development and CI/CD workflows:

Docker Hub - OpenAPI Generator CLI
https://hub.docker.com/r/openapitools/openapi-generator-cli

Originally posted by @uniqueg in #27 (comment)