{RBAC} Polish error message for service principal resolution

[jiasli]

Resolve #12615

When the user creates an app but doesn't create the corresponding service principal, then does role assignment

# pwsh
$AppRegistrationName = 'myapp0317'
$appId = az ad app create --display-name $AppRegistrationName --reply-urls https://api.loganalytics.io/ --available-to-other-tenants false --query 'appId' --output tsv
# az ad sp create --id $appId

$rgName = 'myrg0317'
az group create -n $rgName -l westus
az role assignment create --role Reader --assignee $appId --resource-group $rgName

az role assignment create fails with

No matches in graph database for '64ba0967-d3b7-4346-b7b6-803fdea011a4'

This PR polishes the error message to make it more instructive:

Cannot find user or service principal in graph database for '64ba0967-d3b7-4346-b7b6-803fdea011a4'. If the assignee is an appId, make sure the corresponding service principal is created with 'az ad sp create --id 64ba0967-d3b7-4346-b7b6-803fdea011a4'.

ℹ Clean up:

az ad app delete --id $appId

[yonzhan]

add to S167

[qianwens]