[MM-T5139] Add Standard message priority and system setting test (#29526)

* add Standard message priority and system setting test

* Refactor message priority config and test.

* Refactor to use new priority dialog locators and checks, ensuring default standard option is correctly verified.

* Fix whitespace and formatting in message priority components.

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Co-authored-by: Fume <contact@fumedev.com>
Co-authored-by: Mattermost Build <build@mattermost.com>

e2e-tests/playwright/support/ui/components/index.ts

@@ -21,6 +21,7 @@ import {PostMenu} from './channels/post_menu';
 import {ThreadFooter} from './channels/thread_footer';
 import {EmojiGifPicker} from './channels/emoji_gif_picker';
 import {GenericConfirmModal} from './channels/generic_confirm_modal';
+import {MessagePriority} from './channels/message_priority';
 
 import {ScheduledDraftMenu} from './channels/scheduled_draft_menu';
 import {ScheduledDraftModal} from './channels/scheduled_draft_modal';
@@ -62,6 +63,7 @@ const components = {
     SystemUsersFilterPopover,
     SystemUsersFilterMenu,
     SystemUsersColumnToggleMenu,
+    MessagePriority,
     UserProfilePopover,
 };
 
@@ -80,4 +82,5 @@ export {
     PostDotMenu,
     PostMenu,
     ThreadFooter,
+    MessagePriority,
 };