feat!: Release 3.0.0

[andrewsg]

This release includes the following breaking changes, which are documented in detail in the README.rst file.

As a brief summary, the most broadly relevant changes are:

• Applications that currently import exceptions from the google-resumable-media library (google.resumable_media) should now import those exceptions from google.cloud.storage.exceptions.
• Applications that use positional arguments extensively should verify that the removal of "num_retries" from upload and download methods has not disrupted their argument order.

BEGIN_COMMIT_OVERRIDE
feat!: Media operation retries now work identically to other retries, which may impact default retry settings (#1385) (f3517bf)
feat!: The default checksum strategy for uploads has changed from None to "auto" (#1383) (5375fa0)
feat!: The default checksum strategy for downloads has changed from "md5" to "auto" (#1383) (5375fa0)
feat!: Deprecated positional argument "num_retries" has been removed (#1377) (58b5040)
feat!: Deprecated argument "text_mode" has been removed (#1379) (4d20a8e)
END_COMMIT_OVERRIDE