[Engineering task] Add Credential Probe logic

[gladjohn]

Task type

Development

Description

Add Credential Probe Logic

Solution

• Add a new enum value Credential to ManagedIdentitySource to indicate the use of credential-based managed identity.
• Introduce an asynchronous method GetManagedIdentitySourceAsync in ManagedIdentityApplication to detect the managed identity source in the environment
• Soft deprecate GetManagedIdentitySource @bgavrilMS to confirm

[bgavrilMS]

@gladjohn - let's track internal MSIv2 work in ADO only?