Add an opt-in batch_id_prefix to DataprocCreateBatchOperator so task retries can submit a new Dataproc batch with a unique ID instead of reusing a static batch_id.

Why

When a task retries with the same batch_id, Dataproc can return ALREADY_EXISTS and attach to the old batch. This change provides a built-in retry-safe path without changing existing explicit batch_id behavior.

What changes

• add optional batch_id_prefix parameter
• generate <batch_id_prefix>-<unique_suffix> per task attempt
• keep batch_id and batch_id_prefix mutually exclusive
• keep explicit batch_id behavior unchanged
• update Dataproc operator docs
• add unit tests for:
  • mutual exclusivity
  • prefix-based ID generation
  • execute flow with prefix
  • backward compatibility for explicit batch_id

Test plan

• uv run ruff format providers/google/src/airflow/providers/google/cloud/operators/dataproc.py providers/google/tests/unit/google/cloud/operators/test_dataproc.py
• uv run ruff check --fix providers/google/src/airflow/providers/google/cloud/operators/dataproc.py providers/google/tests/unit/google/cloud/operators/test_dataproc.py
• uv run --project providers/google pytest providers/google/tests/unit/google/cloud/operators/test_dataproc.py::TestDataprocCreateBatchOperator::test_execute providers/google/tests/unit/google/cloud/operators/test_dataproc.py::TestDataprocCreateBatchOperator::test_execute_with_batch_id_prefix providers/google/tests/unit/google/cloud/operators/test_dataproc.py::TestDataprocCreateBatchOperator::test_build_unique_batch_id_from_prefix_preserves_prefix_verbatim providers/google/tests/unit/google/cloud/operators/test_dataproc.py::TestDataprocCreateBatchOperator::test_batch_id_and_batch_id_prefix_are_mutually_exclusive -xvs