Pin the default client image with digest (#227)

This changes the default client image from latest to a pinned digest. It
also enforces that the default image version tag matches the version of
the Netbird dependency.

This makes testing a lot easier and also ensures that we wont get
untested behavior introduced if the client makes a breaking change.

Signed-off-by: Philip Laine <philip.laine@gmail.com>

internal/version/version_test.go

@@ -0,0 +1,33 @@
+package version
+
+import (
+	"os"
+	"slices"
+	"strings"
+	"testing"
+
+	"golang.org/x/mod/modfile"
+
+	"github.com/go-openapi/testify/v2/require"
+)
+
+func TestClientImage(t *testing.T) {
+	t.Parallel()
+
+	b, err := os.ReadFile("../../go.mod")
+	require.NoError(t, err)
+	f, err := modfile.Parse("go.mod", b, nil)
+	require.NoError(t, err)
+	idx := slices.IndexFunc(f.Require, func(r *modfile.Require) bool {
+		return r.Mod.Path == "github.com/netbirdio/netbird"
+	})
+	require.GreaterT(t, idx, -1)
+	modVersion := strings.TrimPrefix(f.Require[idx].Mod.Version, "v")
+
+	clientImg := ClientImage()
+	start := strings.Index(clientImg, ":") + 1
+	end := strings.Index(clientImg, "@")
+	imgVersion := clientImg[start:end]
+
+	require.EqualT(t, modVersion, imgVersion)
+}