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/activity/sqlite/sqlite_test.go

@@ -0,0 +1,53 @@
+package sqlite
+
+import (
+	"fmt"
+	"github.com/netbirdio/netbird/management/server/activity"
+	"github.com/stretchr/testify/assert"
+	"testing"
+	"time"
+)
+
+func TestNewSQLiteStore(t *testing.T) {
+	dataDir := t.TempDir()
+	store, err := NewSQLiteStore(dataDir)
+	if err != nil {
+		t.Fatal(err)
+		return
+	}
+        defer store.Close() //nolint
+
+	accountID := "account_1"
+
+	for i := 0; i < 10; i++ {
+		_, err = store.Save(&activity.Event{
+			Timestamp:   time.Now(),
+			Activity:    activity.PeerAddedByUser,
+			InitiatorID: "user_" + fmt.Sprint(i),
+			TargetID:    "peer_" + fmt.Sprint(i),
+			AccountID:   accountID,
+		})
+		if err != nil {
+			t.Fatal(err)
+			return
+		}
+	}
+
+	result, err := store.Get(accountID, 0, 10, false)
+	if err != nil {
+		t.Fatal(err)
+		return
+	}
+
+	assert.Len(t, result, 10)
+	assert.True(t, result[0].Timestamp.Before(result[len(result)-1].Timestamp))
+
+	result, err = store.Get(accountID, 0, 5, true)
+	if err != nil {
+		t.Fatal(err)
+		return
+	}
+
+	assert.Len(t, result, 5)
+	assert.True(t, result[0].Timestamp.After(result[len(result)-1].Timestamp))
+}