interface: define traffic manager apis

[zhiying-lin]

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• run make reviewable for basic local test
• Read and followed fleet-networking's Code of conduct.
• uses conventional commit messages
• includes documentation
• adds unit tests

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[circy9]

As discussed, we should provide MultiClusterSerivce v1beta to program traffic manager.

MultiClusterSerivce {
  ServiceClass: "TrafficManager"
  Backends {
     {
       ServiceImport: X1
       Weight: 20
     }
     {
       ServiceImport: X2
       Weight: 80
     }
  }
}

Traffic manager should will be auto-created by Fleet under FL_* with reasonable defaults. Users only need to config dns-prefix (== the name of the traffic manager) or we can auto create dns-prefix based on certain patterns.

If needed later, we can allow customers to bring their own traffic manager by allowing an annotation like: trafficmanagerresourceid=x

Here is a traffic manager created via portal where I only specified name, sub, resource group, and routing method:

{
    "id": "/subscriptions/2b03bfb8-e885-4566-a62a-909a11d71692/resourceGroups/liqian-fleet-ga/providers/Microsoft.Network/trafficManagerProfiles/liqian-traffic-manager",
    "name": "liqian-traffic-manager",
    "type": "Microsoft.Network/trafficManagerProfiles",
    "location": "global",
    "tags": {},
    "properties": {
        "profileStatus": "Enabled",
        "trafficRoutingMethod": "Weighted",
        "dnsConfig": {
            "relativeName": "liqian-traffic-manager",
            "fqdn": "liqian-traffic-manager.trafficmanager.net",
            "ttl": 60
        },
        "monitorConfig": {
            "profileMonitorStatus": "Inactive",
            "protocol": "HTTP",
            "port": 80,
            "path": "/",
            "intervalInSeconds": 30,
            "toleratedNumberOfFailures": 3,
            "timeoutInSeconds": 10
        },
        "endpoints": [],
        "trafficViewEnrollmentStatus": "Disabled",
        "maxReturn": 0,
        "recordType": null
    }
}