[Task]: [RRIO] [Throttle] transform that slows down element transmission using Redis

[damondouglas]

What needs to happen?

What needs to happen?

The output of this task is a transform that throttles an incoming PCollection of elements using a Redis based external resource. It uses the Call transform and therefore requires part of its implementation as a dependency. Tests require the use of a Caller implementation of a mock-api.

Measures of Ready

• [Task]: [RRIO] [Call] PTransform executes user custom code without adaptive throttling #28711
• [Task]: [RRIO] [Test] Create test Caller and SetupTeardown interface implementations #28710

Measures of Done

• Tests validate that the maximum rate of outputted elements is approximately equal to a configured value
• Changing to the number of Dataflow workers does not change the transmission rate
• Increasing the rate of element input does not change the transmission rate

Issue Priority

Priority: 2 (default / most normal work should be filed as P2)