* Chore: refactor client.download_blob_to_file (#1052)

* Refactor client.download_blob_to_file

* Chore: clean up code

* refactor blob and client unit tests

* lint reformat

* Rename _prep_and_do_download

* Chore: refactor blob.upload_from_file (#1063)

* Refactor client.download_blob_to_file

* Chore: clean up code

* refactor blob and client unit tests

* lint reformat

* Rename _prep_and_do_download

* Refactor blob.upload_from_file

* Lint reformat

* feature: add 'command' argument to private upload/download interface (#1082)

* Refactor client.download_blob_to_file

* Chore: clean up code

* refactor blob and client unit tests

* lint reformat

* Rename _prep_and_do_download

* Refactor blob.upload_from_file

* Lint reformat

* feature: add 'command' argument to private upload/download interface

* lint reformat

* reduce duplication and edit docstring

* feat: add support for custom headers starting with  metadata op

* add custom headers to downloads in client blob modules

* add custom headers to uploads with tests

* update mocks and tests

* test custom headers support tm mpu uploads

* update tm test

* update test

---------

Co-authored-by: MiaCY <[email protected]>

Fixes #1074 🦕

Source-Link: googleapis/synthtool@d52e638
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:4f9b3b106ad0beafc2c8a415e3f62c1a0cc23cabea115dbe841b848f581cfe99

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>
Co-authored-by: Victor Chudnovsky <[email protected]>

* feat: add Autoclass v2.1 support

* update tests and coverage

* update samples with v2.1 additions

* fix lint

* update samples

…#1172)

Fixes #1071 🦕

As a side-effect, the behavior of this method during a race condition has changed slightly. Previously, if a new object was created while the bucket.delete(force=True) method is running, it would fail, but if a new generation of an existing object was uploaded, it would still succeed. Now it will fail in both cases. Regardless of the exact behavior, please do not use this method on a bucket that is still being updated by another process.

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