feat: Agent assignment policy index page with CRUD actions (#12373)

# Pull Request Template

## Description

This PR incudes new Agent assignment policy index page with CRUD
actions.

Fixes
https://linear.app/chatwoot/issue/CW-5570/feat-assignment-policy-index-page-with-actions

## Type of change

- [x] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

### Loom

https://www.loom.com/share/17ab5ceca4854f179628a3b53f347e5a?sid=cb64e881-57fd-4ae1-921b-7648653cca33

### Screenshots

**Light mode**
<img width="1428" height="888" alt="image"
src="https://github.com/user-attachments/assets/fdbb83e9-1f4f-4432-9e8a-4a8f1b810d31"
/>


**Dark mode**
<img width="1428" height="888" alt="image"
src="https://github.com/user-attachments/assets/f1fb38b9-1150-482c-ba62-3fe63ee1c7d4"
/>
<img width="726" height="495" alt="image"
src="https://github.com/user-attachments/assets/90a6ad55-9ab6-4adb-93a7-2327f5f09c79"
/>


## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/javascript/dashboard/api/assignmentPolicies.js

@@ -0,0 +1,36 @@
+/* global axios */
+
+import ApiClient from './ApiClient';
+
+class AssignmentPolicies extends ApiClient {
+  constructor() {
+    super('assignment_policies', { accountScoped: true });
+  }
+
+  getInboxes(policyId) {
+    return axios.get(`${this.url}/${policyId}/inboxes`);
+  }
+
+  setInboxPolicy(inboxId, policyId) {
+    return axios.post(
+      `/api/v1/accounts/${this.accountIdFromRoute}/inboxes/${inboxId}/assignment_policy`,
+      {
+        assignment_policy_id: policyId,
+      }
+    );
+  }
+
+  getInboxPolicy(inboxId) {
+    return axios.get(
+      `/api/v1/accounts/${this.accountIdFromRoute}/inboxes/${inboxId}/assignment_policy`
+    );
+  }
+
+  removeInboxPolicy(inboxId) {
+    return axios.delete(
+      `/api/v1/accounts/${this.accountIdFromRoute}/inboxes/${inboxId}/assignment_policy`
+    );
+  }
+}
+
+export default new AssignmentPolicies();