fix(cluster-1): data corruption fixes (C4/C5/C8)

- synchandler: combine course date with clock time via time.Date instead
  of adding two absolute Unix epochs, which produced corrupt start times
- tracing: make DeploymentEnvironment configurable via config.Trace
  (defaults to development instead of hardcoded production)
- http: align course handler tracer name to 'kuriweb.http' to match the
  request middleware instrument so spans share the same tracer

internal/common/config/trace.go

@@ -29,10 +29,11 @@ func (t *TraceClientType) UnmarshalText(data []byte) error {
 }
 
 type Trace struct {
-	Endpoint  string          `json:"endpoint"`
-	APIKey    string          `json:"api_key"`
-	APIHeader string          `json:"api_header"`
-	Type      TraceClientType `json:"type"`
+	Endpoint    string          `json:"endpoint"`
+	APIKey      string          `json:"api_key"`
+	APIHeader   string          `json:"api_header"`
+	Type        TraceClientType `json:"type"`
+	Environment string          `json:"environment"`
 
 	ShowMetrics bool `json:"show_metrics"`
 }