chore: Make it easier to search for existing ideas and questions (#994)

When users choose what type of issue to create, Feature and Question
options now link to previous submissions.

Author: claremacrae

.github/ISSUE_TEMPLATE/config.yml

@@ -2,7 +2,7 @@ blank_issues_enabled: false
 contact_links:
   - name: Suggest a new feature
     url: https://github.com/obsidian-tasks-group/obsidian-tasks/discussions/new?category=ideas
-    about: Request a new feature or improvement in the Tasks plugin. Please search existing Ideas first, and up-vote, to avoid Duplicates.
+    about: Request a new feature or improvement in the Tasks plugin.<br>Please [search existing ideas](https://github.com/obsidian-tasks-group/obsidian-tasks/discussions/categories/ideas) first, and up-vote, to avoid duplicates.
   - name: Ask a question
     url: https://github.com/obsidian-tasks-group/obsidian-tasks/discussions/new?category=q-a
-    about: Ask for help with using the Tasks plugin
+    about: Ask for help with using the Tasks plugin.<br>In case your question has been asked before, for quicker results you can [search existing questions](https://github.com/obsidian-tasks-group/obsidian-tasks/discussions/categories/q-a).