[FLINK-8945] [kinesis] Allow customization of KinesisProxy

[kailashhd]

What is the purpose of the change

Allow customization of KinesisProxy. In this case we want to override just the getShardList implementation to use ListShards instead of DescribeStreams.

Brief change log

• Changed the constructor from private to protected for KinesisProxy

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.
Also verified with mvn clean verify.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[kailashhd]

cc @tweise

[tweise]

+1
@StephanEwen can we get this into 1.5.0 ?

[tzulitai]

I'm curious why we don't go directly for replacing describeStreams with listShards. Are there any other concerns for this?

[StephanEwen]

I think this trivial change can be safely merged into 1.5

[tweise]

@StephanEwen thanks for unblocking our work!