events: Implement event system (#4912)

Co-authored-by: Matt Holt <mholt@users.noreply.github.com>

modules/caddyhttp/server.go

@@ -30,6 +30,7 @@ import (
 	"time"
 
 	"github.com/caddyserver/caddy/v2"
+	"github.com/caddyserver/caddy/v2/modules/caddyevents"
 	"github.com/caddyserver/caddy/v2/modules/caddytls"
 	"github.com/caddyserver/certmagic"
 	"github.com/lucas-clemente/quic-go/http3"
@@ -154,9 +155,11 @@ type Server struct {
 	listeners           []net.Listener
 
 	tlsApp       *caddytls.TLS
+	events       *caddyevents.App
 	logger       *zap.Logger
 	accessLogger *zap.Logger
 	errorLogger  *zap.Logger
+	ctx          caddy.Context
 
 	server    *http.Server
 	h3server  *http3.Server