FEATURE: Add paging to the admin users page

[pconrad]

After adding the toggle features to the admin users page, one thing that you'll notice is that as soon as you click on a row, it jumps to another spot.

This is because there is no sorting and paging in the backend for the admin users endpoint.

In addition, the users are not paged; if/when we release this app into real production, the number of users will be too many to display on a single page at once.

Fix this by adding sorting and paging in the backend.

Compare, this code from proj-dining:

  @Operation(summary = "Get a list of all users")
  @PreAuthorize("hasRole('ROLE_ADMIN')")
  @GetMapping("/admin/users")
  public ResponseEntity<String> users() throws JsonProcessingException {

    Iterable<User> users = userRepository.findAll();
    String body = mapper.writeValueAsString(users);
    return ResponseEntity.ok().body(body);
  }

Vs. proj-frontiers: https://github.com/ucsb-cs156/proj-frontiers/blob/main/src/main/java/edu/ucsb/cs156/frontiers/controllers/UsersController.java

@Tag(name = "User information (admin only)")
@RequestMapping("/api/admin/users")
@RestController
public class UsersController extends ApiController {
  @Autowired private UserDataDTOService userDataDTOService;

  /**
   * This method returns a list of all users. Accessible only to users with the role "ROLE_ADMIN".
   *
   * @return a list of all users
   * @throws JsonProcessingException if there is an error processing the JSON
   */
  @Operation(summary = "Get a list of all users")
  @PreAuthorize("hasRole('ROLE_ADMIN')")
  @GetMapping("")
  public Page<UserDataDTO> users(Pageable pageable) throws JsonProcessingException {
    return userDataDTOService.getUserDataDTOs(pageable);
  }
}

But we can't just change this in one step; that would break the frontend.

You'll need to proceed in stages. Each of these is a subissue.

Note that if you need to temporarily remove the ability to toggle users moderator and admin status, that's ok, as long as you can still add/delete moderators in some fashion through either swagger or through a dedicated page for adding and deleting admins and moderators by their email (as is done in frontiers.)

Subissues

• Add an endpoint /api/admin/users/paged that matches the functionality in proj-frontiers. Look into how the userDataDTOService works; you'll need to add that as well.
• Modify the frontend Admin Users Page to incorporate paging. Look at the frontend of frontiers admin users page for a guide as to how to proceed.
• Adjust the code so that the pages of users are always sorted by user id.