Implement role and user management enhancements

- Added MaxIpLimit to roles, allowing for the configuration of simultaneous IP limits for users.
- Updated role creation and update commands to include MaxIpLimit, ensuring proper handling in the application logic.
- Enhanced user management by introducing a DELETE endpoint for user accounts, with appropriate checks to prevent self-deletion.
- Updated documentation to reflect changes in role and user management, clarifying the new IP limit functionality and user deletion process.
- Adjusted related tests to cover new functionality and ensure robust validation of role and user management features.

backend/tests/PnvPanel.IntegrationTests/Configs/ConfigQuotaTests.cs

@@ -40,7 +40,8 @@ public class ConfigQuotaTests(PnvPanelWebApplicationFactory factory)
         var roles = await rolesResponse.ReadAsAsync<List<RoleResponse>>();
         var userRole = roles!.Single(r => r.Name == "user");
 
-        var updateRoleResponse = await adminClient.SendPutJsonAsync($"/api/admin/roles/{userRole.Id}", new { maxConfigs = Quota });
+        var updateRoleResponse = await adminClient.SendPutJsonAsync(
+            $"/api/admin/roles/{userRole.Id}", new { maxConfigs = Quota, maxIpLimit = -1 });
         Assert.Equal(HttpStatusCode.OK, updateRoleResponse.StatusCode);
 
         var registerNodeResponse = await adminClient.PostJsonAsync("/api/admin/nodes", new