chore: have bankSend accept from argument set to default as validator address

[anilhelvaci]

Closes #187
Refs: https://github.com/Agoric/BytePitchPartnerEng/issues/27

tooling improvements

Improve bankSend to accept a parameter as from. Set it to validator account by default so it won't break existing usage.

[anilhelvaci]

Not able to request review (gh disables it). Could you please take a look at this? @turadg

[turadg]

Let's make these improvements in agoric-sdk instead. That'll require Agoric/agoric-sdk#10369

Meanwhile just make a library in z:acceptance

(I recently requested that a new bankSend in a PR be made compatible with the existing signature, which just meant to update it there)