…for writing rows (#284)

* WIP: write client sample

* add sample with nullable types

* add schema for all supported types

* add complex types to code sample

* refactor sample so that it can be tested

* make test assertions more thorough

* fix lint error

* remove done TODO

* address reviewer comments

* fix tag mismatch

* test on multiple regions

* correct comments about why offset exists

* upgrade g-c-b

* WIP: invert stream using BiDi class

* WIP: attempt to use Future for send instead

* WIP: use futures, populated by background consumer

* make sure stream is actually open before returning from open

* copy close implementation from pub/sub

* support extra metadata

* process exceptions, add open timeout

* sort imports

* WIP: unit tests

* drain futures when stream closes

* update docs

* add callbacks to detect when a stream fails

* add unit tests

* add sleep to loop waiting for RPC to be active

* don't freeze if initial RPC fails

* add needed initializations so done() functions

* fail fast when there is a problem with the initial request

* don't inherit concurrent.futures

It's unnecessary and kept resulting in stuff getting stuck.

* add unit test for open timeout

* 🦉 Updates from OwlBot

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* add manual client to docs

* typo in sample comments

* force timeout and metadata to be kwargs

* unify interface for sending row data

* pull stream name from merged request

* require newer proto-plus for copy_from method

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

🤖 I have created a release \*beep\* \*boop\*
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## [2.8.0](https://www.github.com/googleapis/python-bigquery-storage/compare/v2.7.0...v2.8.0) (2021-09-10)


### Features

* add `BigQueryWriteClient` where `append_rows` returns a helper for writing rows ([#284](https://www.github.com/googleapis/python-bigquery-storage/issues/284)) ([2461f63](https://www.github.com/googleapis/python-bigquery-storage/commit/2461f63d37f707c2d634a95d87b8ffc3e4af3686))
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This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please).