Add system activity tracking and event store (#636)

This PR adds system activity tracking. 
The management service records events like 
add/remove peer,  group, rule, route, etc.

The activity events are stored in the SQLite event store
and can be queried by the HTTP API.

management/server/event_test.go

@@ -0,0 +1,63 @@
+package server
+
+import (
+	"github.com/netbirdio/netbird/management/server/activity"
+	"github.com/stretchr/testify/assert"
+	"testing"
+	"time"
+)
+
+func generateAndStoreEvents(t *testing.T, manager *DefaultAccountManager, typ activity.Activity, initiatorID, targetID,
+	accountID string, count int) {
+	for i := 0; i < count; i++ {
+		_, err := manager.eventStore.Save(&activity.Event{
+			Timestamp:   time.Now(),
+			Activity:    typ,
+			InitiatorID: initiatorID,
+			TargetID:    targetID,
+			AccountID:   accountID,
+		})
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+}
+
+func TestDefaultAccountManager_GetEvents(t *testing.T) {
+	manager, err := createManager(t)
+	if err != nil {
+		return
+	}
+
+	accountID := "accountID"
+
+	t.Run("get empty events list", func(t *testing.T) {
+		events, err := manager.GetEvents(accountID, userID)
+		if err != nil {
+			return
+		}
+		assert.Len(t, events, 0)
+		_ = manager.eventStore.Close() //nolint
+	})
+
+	t.Run("get events", func(t *testing.T) {
+		generateAndStoreEvents(t, manager, activity.PeerAddedByUser, userID, "peer", accountID, 10)
+		events, err := manager.GetEvents(accountID, userID)
+		if err != nil {
+			return
+		}
+
+		assert.Len(t, events, 10)
+		_ = manager.eventStore.Close() //nolint
+	})
+
+	t.Run("get events without duplicates", func(t *testing.T) {
+		generateAndStoreEvents(t, manager, activity.UserJoined, userID, "", accountID, 10)
+		events, err := manager.GetEvents(accountID, userID)
+		if err != nil {
+			return
+		}
+		assert.Len(t, events, 1)
+		_ = manager.eventStore.Close() //nolint
+	})
+}