Optimize /org/admin/users/admin_index

app/controllers/users_controller.rb
- Both in the super_user case as well as the non-super_user case, Bullet warnings are addressed by modifying the .includes() args

app/views/paginable/users/_index.html.erb
- This commit removes `presenter = IdentifierPresenter.new(identifiable: user)` and instead accesses `identifier_scheme.name` via the `user` variable. user.identifiers and user.identifiers[i].identifier_scheme are now being eager loaded, whereas IdentifierPresenter was loading IdentifierScheme.for_users for each user.
- Analyzing the code below, we can see how there is no difference between `presenter` and `user` when acccessing `.identifiers` and `.identifiers[i].identifier_scheme`

```
# app/views/paginable/users/_index.html.erb
<% presenter = IdentifierPresenter.new(identifiable: user) %>
<% presenter.identifiers.each do |identifier| %>
  <p><%= identifier.identifier_scheme.name %></p>

# app/presenters/identifier_presenter.rb
class IdentifierPresenter
  attr_reader :schemes, :identifiable

  def initialize(identifiable:)
    @Identifiable = identifiable

    @schemes = load_schemes
  end

  def identifiers
    @identifiable.identifiers
  end
```

app/controllers/users_controller.rb

@@ -21,10 +21,10 @@ def admin_index
         @filter_admin = false
 
         @users = if current_user.can_super_admin?
-                   User.includes(:department, :org, :perms, :roles, :identifiers).page(1)
+                   User.includes(:department, :org, :perms, :roles, identifiers: :identifier_scheme).page(1)
                  else
                    current_user.org.users
-                               .includes(:department, :org, :perms, :roles, :identifiers)
+                               .includes(:department, :perms, :roles, identifiers: :identifier_scheme)
                                .page(1)
                  end
       end

app/views/paginable/users/_index.html.erb

@@ -93,8 +93,7 @@
                     <% end %>
                   </td>
                   <td class="text-center">
-                    <% presenter = IdentifierPresenter.new(identifiable: user) %>
-                    <% presenter.identifiers.each do |identifier| %>
+                    <% user.identifiers.each do |identifier| %>
                       <p><%= identifier.identifier_scheme.name %></p>
                     <% end %>
                   </td>