Implicitly appending extra dimensions for broadcasting

[1ucian0]

A derived discussion of #51 about implicitly appending extra dimensions for broadcasting.

For reference, see #51 (comment)

With the aim to extracting that conversation from the RFC but keep it alive, please continue the discussion in this issue

This discussion might result in one of the following out comes:

• Amending or extending Updated Estimator interface #51
• An agreement on this issue
• It's own RFC

[1ucian0]

cc @levbishop @ihincks

[blakejohnson]

I don't think this deserves an RFC. A Qiskit issue ought to be sufficient.