Use managed identity instead of AzureWebJobsStorage to connect a function app to a storage account

dwhathaway , I think support for user-assigned managed identities is already delivered recently, but it works a little differently -- you have to add additional fx environment variables.  My teammate just discovered this yesterday, so your timing is great :).

https://learn.microsoft.com/en-us/azure/azure-functions/functions-reference?tabs=blob#connecting-to-host-storage-with-an-identity

TL;DR; we had to set
AzureWebJobsStorage__credential: managedidentity
AzureWebJobsStorage__clientId: <client Id of the uami>
AzureWebJobsStorage__accountname: <storage account name>

And use RBAC to assign several roles.
Not sure all these are needed, especially if you aren't using durable functions, but we have `Storage Account Contributor`, `Storage Blob Data Owner` and `Storage Queue Data Contributor` assigned currently and may still be working through some issues with our durable azure function instance.