Consider adding information to ProcessBundleRequest indicating there is no existing state

This allows for skipping all state fetches made during processing this key, preloading the cache with empty values for the key, or extending the cache to include this negative state information to avoid fetches as long as no state is evicted for the key.

This is particularly beneficial in sparse key streaming pipelines where such new keys are common.

It could also be used to avoid fetches in batch pipelines where there is no persisted state.

Imported from Jira [BEAM-13684](https://issues.apache.org/jira/browse/BEAM-13684). Original Jira may contain additional context.
Reported by: scwhittle.