chore: add finalizer for ghost and anonymous users (#3386)

#### What type of PR is this?
/kind improvement
/area core

#### What this PR does / why we need it:
为系统默认用户添加系统保护 finalizer，避免被删除

how to test it?
```shell
curl -u username:password --basic 'http://localhost:8090/api/v1alpha1/users/ghost'
curl -u username:password --basic 'http://localhost:8090/api/v1alpha1/users/anonymousUser'
```
将看到 
```json
"finalizers": [
  "...",
  "system-protection"
]
```
#### Which issue(s) this PR fixes:

Fixes #

#### Special notes for your reviewer:
/cc @halo-dev/sig-halo 
#### Does this PR introduce a user-facing change?

```release-note
None
```

src/main/resources/extensions/user.yaml

@@ -2,6 +2,8 @@ apiVersion: v1alpha1
 kind: User
 metadata:
   name: anonymousUser
+  finalizers:
+    - system-protection
 spec:
   displayName: Anonymous User
   email: anonymous@example.com
@@ -12,6 +14,8 @@ apiVersion: v1alpha1
 kind: User
 metadata:
   name: ghost
+  finalizers:
+    - system-protection
 spec:
   displayName: 已删除用户
   email: ghost@example.com