Tags can't be removed in cloned plugins using decK

To recreate -
step 1:
```
_format_version: "3.0"
cloned_plugins:
- name: new-acl
ref: acl
priority: 1000
tags:
- tag1
- tag2
```
Run `deck gateway sync`, and then
step 2:
```
_format_version: "3.0"
cloned_plugins:
- name: new-acl
ref: acl
priority: 1000
```

Now, running deck gateway sync continues to show drift.

Start with the two declarative configurations in the report and run `deck gateway sync` to reproduce the drift after removing `tags` from `cloned_plugins`. Trace how omitted tags are handled during the sync and diff, and confirm the second sync no longer reports drift.

Written by the indexing model from the issue text.