[Example] Move "work" out of the trigger functions for interest accrual/payment

[MerrionComputing]

The HTTP trigger functions for these two get the set of all the accounts to process - this is innefficient and runs the risk of the trigger function timing out. (20k entities seems to be the limit for this)

It should be changed such that a durable functions activity does that part of the job so that iot does not time out and can potentially be performed in parallel.