streaming: create stream ingestion job

[pbardea]

A new type of job is needed to consume a partitioned stream.

The job should:

• Using a streaming client, fetch the stream partitions from a "stream address".
• Create a DistSQL flow of stream partition ingestion processors (introduced in streaming: add stream partition ingestion processors #57398)

The initial version will explicitly not require coordination of resolved timestamps across processors to keep track of the low-watermark.