Dsub

This release includes:

- `dsub`
- (New) (In Development) Implemented `google-batch` provider.
- Note that this is not yet feature parity with the other providers.
- See [Get started with Batch](https://cloud.google.com/batch/docs/get-started) for details on Google Cloud Batch.
- `setup.py`: Update dsub dependent libraries to pick up newer versions.
- Update providers to allow a mount other than `/mnt/data`.
- Fix documentation about mounting an existing disk
- Fix unit test `socket.timeout` alias issue with Python 3.10

This release includes:

* `dsub`
* Add support for mounting an existing disk read-only to a pipeline VM
* `setup.py`: Update dsub dependent libraries to pick up newer versions
* Documentation
* Include documenting the Cloud SDK as a requirement for the local provider

This release includes:

* `dsub`
* Add support for Toronto, Delhi, Melbourne, and Warsaw regions
* `setup.py`: Update dsub dependent libraries to pick up newer versions.

This release includes small maintenance updates:

- `dsub`
- Quiet a warning about 'oauth2client' (which `dsub` no longer uses).
- Fix one other instance of `cache_discovery=True` raising `ImportError`.
- Add `flush` method to `_Printer`.
- Run `pytype` on `dsub`, and fix type errors
- `setup.py`: Update `dsub` dependent libraries to pick up newer versions.
- Update `tenacity` version

This release includes:

- `dsub`
- Implement `--block-external-network` to support network-sandboxed user action.
- `setup.py`: Update `dsub` dependent libraries to pick up newer versions.
- Check for python or python3 executable in local runner script. Also fix error handling for the first "write_event".
- Add zones for Seoul, Jakarta, Salt Lake City, and Las Vegas
- Documentation
- Rename references to the `master` branch to the `main` branch.

This release includes:

- `dsub`
- Update parsing of worker assigned event text to account for changes in Pipelines API.
- Hide the `--nvidia-driver-version` flag as it is now ignored by the Pipelines API (since Sept 2020).

- Documentation
- Fix link to accelerator API doc in README.
- Fix documentation that assumed `TMPDIR` is `/tmp`.
- Mention SSH from the browser in troubleshooting docs.

- Tests
- Add e2e test that confirms GPU is installed when `--accelerator-type` and `--accelerator-count` is used.
- Removed infrequently used environment variables, `CHECK_RESULTS_ONLY` and `ALLOW_DIRTY_TESTS`, from `dsub` tests.