feat: anonymous usage telemetry via oss-telemetry

Send a single fire-and-forget ping at startup to help track adoption
and version spread. No persistent identifiers are collected.

Adds main.Version var (defaulting to "dev") so the existing goreleaser
ldflags injection (-X main.Version={{.Version}}) now binds to a real
symbol.

Opt out via any of:
  DO_NOT_TRACK=1
  OSS_TELEMETRY_DISABLED=1
  KUBEMIRROR_DISABLE_TELEMETRY=1

cmd/kubemirror/main.go

@@ -27,8 +27,14 @@ import (
 	"github.com/lukaszraczylo/kubemirror/pkg/controller"
 	"github.com/lukaszraczylo/kubemirror/pkg/discovery"
 	"github.com/lukaszraczylo/kubemirror/pkg/filter"
+	telemetry "github.com/lukaszraczylo/oss-telemetry"
 )
 
+// Version is the build version. Set via ldflags during build:
+//
+//	-X main.Version=v1.2.3
+var Version = "dev"
+
 var (
 	scheme   = runtime.NewScheme()
 	setupLog = ctrl.Log.WithName("setup")
@@ -57,6 +63,8 @@ func makeCacheSyncChecker(c cache.Cache, ctx context.Context, logger logr.Logger
 }
 
 func main() {
+	telemetry.Send("kubemirror", Version)
+
 	var (
 		metricsAddr           string
 		probeAddr             string