Implement automatic code regeneration for OpenAPI changes

[vilmosnagy]

We should implement a solution to automatically regenerate the generated code. The automatic regeneration should happen in two scenarios:

1. Whenever the openapi.yaml file changes in the p2-inc/phasetwo-docs repository
2. On a scheduled basis (e.g., weekly/monthly) to pick up new OpenAPI Generator releases

Initially, the workflow should open a pull request to allow for manual review of the generated changes. After validating that the workflow is stable and requires minimal manual intervention, we can transition to automatically merging to main and releasing the changes in a future issue.

Investigation Needed

• Design a GitHub Actions workflow that supports both update triggers
• Investigate cross-repository triggers to detect changes in p2-inc/phasetwo-docs and open PRs in this repository

[vilmosnagy]

Motivated by p2-inc/phasetwo-docs#305