Add "interest accrued/paid" to bank example

[MerrionComputing]

Add to the demo Bank Account example events for accruing and paying interest to demonstrate how the "as of" projections can be used to get around concurrency issues.

[MerrionComputing]

For interest accrual we need to prevent two accruals being written for one day.

For interest payment we don't need to do that as the interest due should be zero after the first payment.

[MerrionComputing]

For interest being paid on an overdrawn account, if the amount to pay would exceed the overdraft limit we need to extend the overdraft to cover that limit.

[MerrionComputing]

Error message:

Orchestrator function 'AccrueInterestForAllAccounts' failed:-
The function 'AccrueInterestForSpecificAccount' doesn't exist, is disabled, 
or is not an orchestrator function. 
Additional info: The following are the known orchestrator functions: 'AccrueInterestForAllAccounts'.

It looks like it should be calling an activity, not an orchestration...

{
  "generatedBy": "Microsoft.NET.Sdk.Functions-1.0.29",
  "configurationSource": "attributes",
  "bindings": [
    {
      "type": "activityTrigger",
      "name": "accrueInterestContext"
    }
  ],
  "disabled": false,
  "scriptFile": "../bin/RetailBank.AzureFunctionApp.dll",
  "entryPoint": "RetailBank.AzureFunctionApp.AccountFunctions.AccrueInterestForSpecificAccount"
}

[MerrionComputing]

Added (and documented) using azure durable function orchestration