local live backup support (#185)

* live backup first commit

* exclude lock file in backup

* create path if not exist for backup

Co-authored-by: yash <yash.chandra@grabpay.com>
Co-authored-by: James Mills <prologic@shortcircuit.net.au>

internal/metadata/metadata.go

@@ -0,0 +1,21 @@
+package metadata
+
+import (
+	"os"
+
+	"github.com/prologic/bitcask/internal"
+)
+
+type MetaData struct {
+	IndexUpToDate bool `json:"index_up_to_date"`
+}
+
+func (m *MetaData) Save(path string, mode os.FileMode) error {
+	return internal.SaveJsonToFile(m, path, mode)
+}
+
+func Load(path string) (*MetaData, error) {
+	var m MetaData
+	err := internal.LoadFromJsonFile(path, &m)
+	return &m, err
+}