Add description to text/plain emails

Added to
* new_issue_email
* new_merge_request_email

CHANGELOG

@@ -66,6 +66,7 @@ v 8.11.0 (unreleased)
   - Sensible state specific default sort order for issues and merge requests !5453 (tomb0y)
   - Fix RequestProfiler::Middleware error when code is reloaded in development
   - Catch what warden might throw when profiling requests to re-throw it
+  - Add description to new_issue email and new_merge_request_email in text/plain content type. !5663 (dixpac)
   - Speed up and reduce memory usage of Commit#repo_changes, Repository#expire_avatar_cache and IrkerWorker
 
 v 8.10.4 (unreleased)

app/views/notify/new_issue_email.text.erb

@@ -3,3 +3,5 @@ New Issue was created.
 Issue <%= @issue.iid %>: <%= url_for(namespace_project_issue_url(@issue.project.namespace, @issue.project, @issue)) %>
 Author:    <%= @issue.author_name %>
 Assignee:  <%= @issue.assignee_name %>
+
+<%= @issue.description %>

app/views/notify/new_merge_request_email.text.erb

@@ -6,3 +6,5 @@ New Merge Request <%= @merge_request.to_reference %>
 Author:    <%= @merge_request.author_name %>
 Assignee:  <%= @merge_request.assignee_name %>
 
+<%= @merge_request.description %>
+