Update Slack authorization page UI

What does this MR do and why?

Update UI to include more information on what permissions the app will use.

Also removes the settings search bar which isn't very useful on this page.

Changelog: changed

Screenshots or screen recordings

Page	Before	After
Slack authorization
Chat names index

How to set up and validate locally

1. Apply this diff to allow rendering the page without setting up a Slack application:

diff --git a/app/controllers/profiles/chat_names_controller.rb b/app/controllers/profiles/chat_names_controller.rb
index ae757c30d1cd..d17574cedccb 100644
--- a/app/controllers/profiles/chat_names_controller.rb
+++ b/app/controllers/profiles/chat_names_controller.rb
@@ -53,11 +53,11 @@ def delete_chat_name_token
   end
 
   def chat_name_params
-    @chat_name_params ||= chat_name_token.get || render_404
+    @chat_name_params ||= chat_name_token.get || { chat_name: 'something' }
   end
 
   def chat_name_token
-    return render_404 unless params[:token] || render_404
+    # return render_404 unless params[:token] || render_404
 
     @chat_name_token ||= Gitlab::ChatNameToken.new(params[:token])
   end

1. Go to http://127.0.0.1:3000/-/profile/chat_names/new?token=randomstring.
2. Go to the index page http://127.0.0.1:3000/-/profile/chat_names.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

Related to #388070 (closed)