Allow to get an existing Microsoft.Graph/groups using its objectId, instead of only its uniqueName

Is your feature request related to a problem? Please describe.

For some scenarios it's mandated by a central IT department that reference to certain existing security groups are made by objectId. Usually this is mandated for those security groups prolifically referenced throughout the enterprise, and maintained by a central IT function. This central IT functions reserving the right to rename those security groups as need arises.

This is very much a real world scenario that we face at the company I work for.

Describe the solution you'd like

To be able to reference an existing group using the following syntax:

resource directoryReadersGroup 'Microsoft.Graph/groups@v1.0' existing = {
    objectId: 'da338f18-c126-4bf2-85e6-400f3c63cf8c'
}