FEATURE: Create a link to start a new chat (#25722)

This feature adds the functionality to start a new chat directly from the URL using query params.

The format is: /chat/new-message?recipients=buford,jona

The initial version of this feature allows for the following:

- Open an existing direct message channel with a single user
- Create a new direct message channel with a single user (and auto redirect)
- Create or open a channel with multiple users (and auto redirect)
- Redirects to chat home if the recipients param is missing

plugins/chat/spec/system/page_objects/chat/chat.rb

@@ -91,6 +91,16 @@ module PageObjects
         PageObjects::Pages::ChatBrowse.new.has_finished_loading?
       end
 
+      def visit_new_message(recipients)
+        if recipients.is_a?(Array)
+          recipients = recipients.map(&:username).join(",")
+        elsif recipients.respond_to?(:username)
+          recipients = recipients.username
+        end
+
+        visit("/chat/new-message?recipients=#{recipients}")
+      end
+
       def has_finished_loading?
         has_no_css?(".chat-channel--not-loaded-once")
         has_no_css?(".chat-skeleton")