Update the function app to runtime 4.x for continued support

[gregtampa]

https://learn.microsoft.com/en-us/azure/azure-functions/migrate-version-3-version-4?tabs=net6-in-proc%2Cazure-cli%2Cwindows&pivots=programming-language-csharp

Update the function app to runtime 4.x as this app is using 3.x and will be discontinued in Dec 3rd, 2022 according to Microsoft.