feat: Add snapshot API definitions for backup and restore

issue: milvus-io/milvus#44358
Add snapshot-related protobuf definitions and RPC services:
- Add snapshot privilege definitions in common.proto
- Add snapshot RPC services in milvus.proto
- Add snapshot.proto with request/response messages
- Update proto generation script to include snapshot files

This provides the foundation for implementing snapshot-based backup and restore
functionality with proper privilege control.

Signed-off-by: Wei Liu <[email protected]>

Author: weiliu1031

go-api/commonpb/common.pb.go

@@ -327,6 +327,15 @@ enum MsgType {
 
     /* WAL group */
     AlterWAL = 2000;
+
+    /* Snapshot */
+    CreateSnapshot = 2100;
+    DropSnapshot = 2101;
+    ListSnapshots = 2102;
+    DescribeSnapshot = 2103;
+    RestoreSnapshot = 2104;
+    GetRestoreSnapshotState = 2105;
+    ListRestoreSnapshotJobs = 2106;
 }
 
 message MsgBase {
@@ -476,6 +485,12 @@ enum ObjectPrivilege {
     PrivilegeRemoveFileResource = 73;
     PrivilegeListFileResources = 74;
     PrivilegeUpdateReplicateConfiguration = 78;
+
+    PrivilegeCreateSnapshot = 79;
+    PrivilegeDropSnapshot = 80;
+    PrivilegeDescribeSnapshot = 81;
+    PrivilegeListSnapshots = 82;
+    PrivilegeRestoreSnapshot = 83;
 }
 
 message PrivilegeExt {