[Workflow editor] Add basic placeholder building blocks

[ohltyler]

Develop interfaces and implement some of the basic building blocks with proposed inputs/outputs/fields for support of the initial neural search use cases

[ohltyler]

Update 4/2: tuned the issue to specifically be initial building blocks for the first use cases - semantic/hybrid/multi-modal search, etc.

[ohltyler]

Scoped to different variations of the same ML inference processor block to be applied to initial use cases. Marking as complete.