FLIP proposal to expand Access Streaming API (#229)

* Added first part of document

* Added extended descriptions to endpoints.

* Added performance and dependencies

* Added first draft for resources changes and movement. Left ref links for now.

* Cleaned up. Added disscussion questions

* Added question

* Cleaned up questions. End up document

* Renamed file

* Added FLIP number

* Apply suggestions from code review

Co-authored-by: Peter Argue <[email protected]>

* Changed to SubscribeBlockHeaders

* Changed to SubscribeBlockDigests

* Added argument to SubscribeBlock

* Added arguments to SubscribeAccountStatuses

* Added expected responces

* Added explanation to arguments

* Extend WS description.

* Added heartbeat

* Apply suggestions from code review

Co-authored-by: Peter Argue <[email protected]>

* fixed remarks

* Renamed SeqNumber to MessageeIndex

* Fix incorrect FLIP numbering error

I didn't realize the number was supposed to be the GH Issue number mapping to this FLIP in this repo

* Fixed sponsor field

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Co-authored-by: Peter Argue <[email protected]>
Co-authored-by: Jerome Pimmel <[email protected]>