Add a batch write flow control example for Bigtable

[kongweihan]

Description

Add a batch write flow control example for Bigtable

Checklist

• [x] I have followed Sample Format Guide
• [x] pom.xml parent set to latest shared-configuration
• [X] Appropriate changes to README are included in PR
• [] These samples need a new API enabled in testing projects to pass (let us know which ones)
• [] These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• [x] Tests pass: mvn clean verify required
• [x] Lint passes: mvn -P lint checkstyle:check required
• [x] Static Analysis: mvn -P lint clean compile pmd:cpd-check spotbugs:check advisory only
• [] This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• [] This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• [x] Please merge this PR for me once it is approved

[snippet-bot[bot]]

Here is the summary of changes.

You are about to add 3 region tags.

- [bigtable/beam/batch-write-flow-control-example/src/main/java/bigtable/BatchWriteFlowControlExample.java:19](https://github.com/kongweihan/java-docs-samples/blob/a14b37d54a8e634f449625b31032142cf4dae8ed/bigtable/beam/batch-write-flow-control-example/src/main/java/bigtable/BatchWriteFlowControlExample.java#L19), tag `bigtable_beam_batch_write_flow_control_imports` - [bigtable/beam/batch-write-flow-control-example/src/main/java/bigtable/BatchWriteFlowControlExample.java:110](https://github.com/kongweihan/java-docs-samples/blob/a14b37d54a8e634f449625b31032142cf4dae8ed/bigtable/beam/batch-write-flow-control-example/src/main/java/bigtable/BatchWriteFlowControlExample.java#L110), tag `bigtable_beam_batch_write_flow_control_cloudbigtableio` - [bigtable/beam/batch-write-flow-control-example/src/main/java/bigtable/BatchWriteFlowControlExample.java:134](https://github.com/kongweihan/java-docs-samples/blob/a14b37d54a8e634f449625b31032142cf4dae8ed/bigtable/beam/batch-write-flow-control-example/src/main/java/bigtable/BatchWriteFlowControlExample.java#L134), tag `bigtable_beam_batch_write_flow_control_bigtableio`

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[kongweihan]

Hello, Please address the following questions:

1. We ask to have a single code sample per file. This code looks like showing two code samples. What is this code sample demonstrates?
2. This code sample does not have regional tags. What documentation use it?
3. We do not host code samples without tests. What is a reason for lack of tests?

I think I've resolved the above comments. Any more thoughts on this? @minherz Thanks!

[kongweihan]

@minherz Is there any other comments that I can address? Thank you!

[kongweihan]

lgtm. please review this regional tag in http://devrel if you have access

What do you mean by reviewing it in http://devrel? IIUC after submit I'll notify our tech writer about the tags.

There're 2 pending reviewers in this PR, do you know how may I contact these reviewers? Thanks!

[minherz]

What do you mean by reviewing it in http://devrel? IIUC after submit I'll notify our tech writer about the tags.

I mean that the product (first word in the tag) is a registered product and there is no duplication or overlap with other code samples using the same region tag.

There're 2 pending reviewers in this PR, do you know how may I contact these reviewers? Thanks!

I think that first matter of business should be to fix all failed Kokoro checks. You can ping @billyjacobson in the comment after that.