[AIP-94] airflowctl tasks: add TasksOperations and TaskInstancesOperations to operations.py

### Body

Add TasksOperations and TaskInstancesOperations classes to airflowctl/api/operations.py.
These return the API response directly with no transformation — CLI commands are auto-generated
by CommandFactory. Also unblocks Issue C (custom task commands), which reuses the same operations.

All REST API endpoints already exist.

## Operations to add

On top of https://github.com/apache/airflow/issues/61547, verify the existence, and please don't duplicate

Note
- anything work with single endpoint under operation.py
- anything needs multiple endpoint or transformation goesn ctl/commands
- including unit and integration test under airflow-ctl-tests/

### Committer

- [x] I acknowledge that I am a maintainer/committer of the Apache Airflow project.