[v3] Finalize store API

[jhamman]

The discussion in #1686 highlighted a number of good improvements to the store API. This ticket tracks getting those updated in the design doc and implemented.

• update design doc
• update store base class and current implementations.
  • Async Generators (feature(store): list_* -> AsyncGenerators #1844)
  • Store Open/Close/Mode
  • [ ] Store metadata methods (Feature/store metadata methods #1851)