docs: remove troubleshooting issue template (#25156)

Remove the Troubleshooting issue template. Add contact links to
StackOverflow, Gitter and Google Groups.

The support request [Saved
Reply](https://github.com/angular/angular/blob/main/docs/SAVED_REPLIES.md)
summarizes well why issues are not the best place to help support help.

>>>
Hello, we reviewed this issue and determined that it doesn't fall into the bug report or feature request category. This issue tracker is not suitable for support requests, please repost your issue on [StackOverflow](https://stackoverflow.com/) using tag `angular`.

If you are wondering why we don't resolve support issues via the issue tracker, please [check out this explanation](https://github.com/angular/angular/blob/main/CONTRIBUTING.md#question).

(cherry picked from commit 7ba9fa7)

Author: zarend

.github/ISSUE_TEMPLATE/config.yml

@@ -3,3 +3,12 @@ contact_links:
   - name: Angular Framework
     url: https://github.com/angular/angular/issues/new
     about: Issues and feature requests for Angular Framework
+  - name: StackOverflow
+    url: https://stackoverflow.com/questions/tagged/angular-material2
+    about: Extended community of users can provide troubleshooting help
+  - name: Gitter
+    url: https://gitter.im/angular/material2
+    about: Extended community of users can provide troubleshooting help
+  - name: Google Groups
+    url: https://groups.google.com/forum/#!forum/angular-material2
+    about: Extended community of users can provide troubleshooting help