[Microsoft.App/managedEnvironments]: add identity block

### Resource Type

Microsoft.App/managedEnvironments

### Api Version

2024-03-01

### Issue Type

Inaccurate property type(s)

### Other Notes

Container App Environments support the assignment of managed identities within the portal, but not within the Bicep code. If an identity block is added, it is passed to the API and is successfully associated with the environment.
It is marked as "The property "identity" does not exist in the resource or type definition, although it might still be valid." when validating the code.
Could support for the identity block be added to BIcep?

### Bicep Repro

resource existingManagedIdentity 'Microsoft.ManagedIdentity/userAssignedIdentities@2023-01-31' existing = {
name: managedIdName
}
...
resource containerAppEnv 'Microsoft.App/managedEnvironments@2024-03-01' = {
name: caeName
location: location
identity: {
type: 'UserAssigned'
userAssignedIdentities: {
'${existingManagedIdentity.id}': {}
}
}
tags: tags
properties: {
peerAuthentication: {
mtls: {
enabled: false
}
}
workloadProfiles: [
{
workloadProfileType: 'Consumption'
name: 'Consumption'
}
{
workloadProfileType: workloadProfileType
name: workloadProfileName
minimumCount: workloadProfileTypeMin
maximumCount: workloadProfileTypeMax
}
]
vnetConfiguration: {
infrastructureSubnetId: existingVnet::existingSubnet.id
internal: isInternal
}
appLogsConfiguration: {
destination: 'log-analytics'
logAnalyticsConfiguration: {
customerId: existinglogAnalyticsWorkspace.properties.customerId
sharedKey: existinglogAnalyticsWorkspace.listKeys().primarySharedKey
}
}
}
}

### Confirm

- [X] I have read the troubleshooting guide and looked for duplicates.

Start at the Microsoft.App/managedEnvironments resource definition for API version 2024-03-01 and inspect how identity properties are represented. Use the supplied Bicep repro as the validation case; done means the identity block is accepted without a property-definition warning for that API version.

Written by the indexing model from the issue text.