Adding methods for default / implicit behavior in storage.

Source-Link: https://togithub.com/googleapis/synthtool/commit/cb960373d12d20f8dc38beee2bf884d49627165e
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:2d816f26f728ac8b24248741e7d4c461c09764ef9f7be3684d557c9632e46dbd

…p/templates/python_library/.kokoro (#570)

Source-Link: https://togithub.com/googleapis/synthtool/commit/bb171351c3946d3c3c32e60f5f18cee8c464ec51
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:f62c53736eccb0c4934a3ea9316e0d57696bb49c1a7c86c726e9bb8a2f87dadf

…p/templates/python_library/.kokoro (#570)

Source-Link: https://togithub.com/googleapis/synthtool/commit/bb171351c3946d3c3c32e60f5f18cee8c464ec51
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:f62c53736eccb0c4934a3ea9316e0d57696bb49c1a7c86c726e9bb8a2f87dadf

Source-Link: googleapis/synthtool@50db768
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:e09366bdf0fd9c8976592988390b24d53583dd9f002d476934da43725adbb978

Co-authored-by: Dov Shlachter <dovs@google.com>

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:
- [ ] Make sure to open an issue as a [bug/issue](https://github.com/googleapis/python-storage/issues/new/choose) before writing your code!  That way we can discuss the change, evaluate designs, and agree on the general idea
- [ ] Ensure the tests and linter pass
- [ ] Code coverage does not decrease (if any source code was changed)
- [ ] Appropriate docs were updated (if necessary)

Fixes #565 🦕

🤖 I have created a release \*beep\* \*boop\*
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### [1.42.1](https://www.github.com/googleapis/python-storage/compare/v1.42.0...v1.42.1) (2021-09-07)


### Bug Fixes

* do not append duplicates to user agent string ([#570](https://www.github.com/googleapis/python-storage/issues/570)) ([57cf3a1](https://www.github.com/googleapis/python-storage/commit/57cf3a1f27292939ed097ef8afa3f4392c4b83e0))


### Documentation

* pass explicit 'client' in '{Blob.Bucket}.from_string' examples ([#545](https://www.github.com/googleapis/python-storage/issues/545)) ([6eff22d](https://www.github.com/googleapis/python-storage/commit/6eff22db0e8c8689208ee52fa815f3ea00675094))
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