timerService: hard-coded boardId (boardAux?)

[dckc]

idea: put the contract terms in boardAux under the boardId of the contract instance

[dckc]

Meanwhile, having the timer service on the board at all conflicts with the goal of making it closely held:

• make TimerService closely held by contracts: remove from terms, Board, home object Agoric/agoric-sdk#5799

So we might need a walletFactory enhancement to be able to make offers with non-trivial exit conditions.

[dckc]

maybe get the board ID from process.env?
(12-factor style)