feat: Add etcd database support

improve concurrent access and high availability of aptly with the help of the characteristics of etcd

database/etcddb/batch.go

@@ -0,0 +1,34 @@
+package etcddb
+
+import (
+	"github.com/aptly-dev/aptly/database"
+	clientv3 "go.etcd.io/etcd/client/v3"
+)
+
+type EtcDBatch struct {
+	db *clientv3.Client
+}
+
+type WriteOptions struct {
+	NoWriteMerge bool
+	Sync         bool
+}
+
+func (b *EtcDBatch) Put(key, value []byte) (err error) {
+	_, err = b.db.Put(Ctx, string(key), string(value))
+	return
+}
+
+func (b *EtcDBatch) Delete(key []byte) (err error) {
+	_, err = b.db.Delete(Ctx, string(key))
+	return
+}
+
+func (b *EtcDBatch) Write() (err error) {
+	return
+}
+
+// batch should implement database.Batch
+var (
+	_ database.Batch = &EtcDBatch{}
+)