feat: create manual client for Write API

[yirutang]

Fixes #111 ☕️

A StreamWriter that provides built-in capabilities to help making bi-di streaming client easy to use:

• handle batching of messages;
• controlling memory utilization (through flow control);
• automatic connection re-establishment;
• request cleanup (only keeps write schema on first request in the stream).

Example:
WriteStream writeStream =
client.createWriteStream(
CreateWriteStreamRequest.newBuilder()
.setParent(tableId2)
.setWriteStream(WriteStream.newBuilder().setType(WriteStream.Type.PENDING).build())
.build());
StreamWriter streamWriter = StreamWriter.newBuilder(writeStream.getName()).build();
ApiFuture response =
streamWriter.append(
createAppendRequestComplicateType(writeStream.getName(), new String[] {"aaa"})
.setOffset(Int64Value.of(0L))
.build());
assertEquals(0, response.get().getOffset());
streamWriter.shutdown();
}

[codecov]

Codecov Report

Merging #112 into master will increase coverage by 1.52%.
The diff coverage is 81.05%.

@@             Coverage Diff              @@
##             master     #112      +/-   ##
============================================
+ Coverage     72.36%   73.88%   +1.52%     
- Complexity      281      319      +38     
============================================
  Files            39       42       +3     
  Lines          1809     2229     +420     
  Branches          4       70      +66     
============================================
+ Hits           1309     1647     +338     
- Misses          496      552      +56     
- Partials          4       30      +26

Impacted Files	Coverage Δ	Complexity Δ
...google/cloud/bigquery/storage/v1alpha2/Waiter.java	72.54% <72.54%> (ø)	14 <14> (?)
.../cloud/bigquery/storage/v1alpha2/StreamWriter.java	81.17% <81.17%> (ø)	28 <28> (?)
...igquery/storage/v1alpha2/ProtoSchemaConverter.java	93.54% <93.54%> (ø)	6 <6> (?)
...igquery/storage/v1beta1/BigQueryStorageClient.java	68.75% <0%> (-1.84%)	16% <0%> (-3%)
...ery/storage/v1beta1/BaseBigQueryStorageClient.java	68.75% <0%> (-1.84%)	16% <0%> (-3%)
...d/bigquery/storage/v1beta2/BigQueryReadClient.java	51.51% <0%> (-1.43%)	8% <0%> (-1%)
.../cloud/bigquery/storage/v1/BigQueryReadClient.java	51.51% <0%> (-1.43%)	8% <0%> (-1%)
...ud/bigquery/storage/v1/BaseBigQueryReadClient.java	54.54% <0%> (-1.34%)	9% <0%> (-1%)
...gquery/storage/v1beta2/BaseBigQueryReadClient.java	54.54% <0%> (-1.34%)	9% <0%> (-1%)
...ery/storage/v1beta2/stub/GrpcBigQueryReadStub.java	89.74% <0%> (-0.62%)	9% <0%> (-1%)
... and 15 more

---

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[stephaniewang526]

please take a look at the various build failures.

[stephaniewang526]

As a general note, all public methods need to be documented clearly in accompanying Java doc to help developers understand what the inputs, outputs, exceptions, etc are. I see a number of public methods without Java doc. Please make sure to put them in.

[yirutang]

PTAL