tailcfg: add ServiceName

Rather than using a string everywhere and needing to clarify that the
string should have the svc: prefix, create a separate type for Service
names.

Updates tailscale/corp#24607

Change-Id: I720e022f61a7221644bb60955b72cacf42f59960
Signed-off-by: Adrian Dewhurst <adrian@tailscale.com>

ipn/ipn_clone.go

@@ -106,7 +106,7 @@ func (src *ServeConfig) Clone() *ServeConfig {
 		}
 	}
 	if dst.Services != nil {
-		dst.Services = map[string]*ServiceConfig{}
+		dst.Services = map[tailcfg.ServiceName]*ServiceConfig{}
 		for k, v := range src.Services {
 			if v == nil {
 				dst.Services[k] = nil
@@ -133,7 +133,7 @@ func (src *ServeConfig) Clone() *ServeConfig {
 var _ServeConfigCloneNeedsRegeneration = ServeConfig(struct {
 	TCP         map[uint16]*TCPPortHandler
 	Web         map[HostPort]*WebServerConfig
-	Services    map[string]*ServiceConfig
+	Services    map[tailcfg.ServiceName]*ServiceConfig
 	AllowFunnel map[HostPort]bool
 	Foreground  map[string]*ServeConfig
 	ETag        string