Allow compilation without CGO (#4266)

`ent` driver gives a normal error if the binary is compiled without CGO, but with our custom SQL driver Dex just fails to compile.

```
# github.com/dexidp/dex/cmd/dex
cmd/dex/config.go:273:26: undefined: sql.SQLite3
cmd/dex/config.go:315:43: undefined: sql.SQLite3
```

Signed-off-by: Maksim Nabokikh <maksim.nabokikh@flant.com>
Signed-off-by: Maksim Nabokikh <max.nabokih@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

storage/sql/sqlite_no_cgo.go

@@ -0,0 +1,19 @@
+//go:build !cgo
+// +build !cgo
+
+// This is a stub for the no CGO compilation (CGO_ENABLED=0)
+
+package sql
+
+import (
+	"fmt"
+	"log/slog"
+
+	"github.com/dexidp/dex/storage"
+)
+
+type SQLite3 struct{}
+
+func (s *SQLite3) Open(logger *slog.Logger) (storage.Storage, error) {
+	return nil, fmt.Errorf("SQLite storage is not available: binary compiled without CGO support. Recompile with CGO_ENABLED=1 or use a different storage backend.")
+}