chore(portal): Save MAU billing for a future feature update (#4414)

Just updating the UI to be a bit more consistent.

Will be nice to offer MAU billing along with directory sync to Team plan
in a future feature release.

<img width="635" alt="Screenshot 2024-03-31 at 8 49 01 AM"
src="https://github.com/firezone/firezone/assets/167144/4a309035-527b-4d4f-96d3-d5b8abeaa03b">

elixir/apps/web/lib/web/live/settings/billing.ex

@@ -102,7 +102,7 @@ defmodule Web.Settings.Billing do
 
           <.vertical_table_row :if={not is_nil(@account.limits.monthly_active_users_count)}>
             <:label>
-              <p>Seats</p>
+              <p>Users</p>
             </:label>
             <:value>
               <span class={[
@@ -112,7 +112,7 @@ defmodule Web.Settings.Billing do
                 <%= @active_users_count %> used
               </span>
               / <%= @account.limits.monthly_active_users_count %> allowed
-              <p class="text-xs">users with at least one device signed-in within last month</p>
+              <p class="text-xs">Includes both admins and regular users.</p>
             </:value>
           </.vertical_table_row>