feat(server): online session history with configurable stats window (#1243)

Add persisted online sessions, configurable retention and online history statistics with lifecycle, recovery, timezone and concurrency regression coverage.

Co-authored-by: naiba/CloudCode <hi+cloudcode@nai.ba>

cmd/dashboard/http_header_timeout.go

@@ -0,0 +1,14 @@
+package main
+
+import (
+	"net/http"
+	"time"
+)
+
+const dashboardReadHeaderTimeout = 5 * time.Second
+
+func newDashboardHTTPServer(handler http.Handler) *http.Server {
+	// ReadHeaderTimeout protects incomplete HTTP/1 requests and is cleared after
+	// headers. Unlike ReadTimeout it does not impose a lifetime on HTTP/2 streams.
+	return &http.Server{Handler: handler, ReadHeaderTimeout: dashboardReadHeaderTimeout}
+}