Clean up at .github due to repo rename (#23580)

* update .github after repo rename

* update

* Update PULL_REQUEST_TEMPLATE.md

---------

Co-authored-by: M-ZubairAhmed <m-zubairahmed@protonmail.com>
Co-authored-by: Mattermost Build <build@mattermost.com>

webapp/channels/.github/PULL_REQUEST_TEMPLATE.md

@@ -12,16 +12,15 @@ A description of what this pull request does.
 
 #### Ticket Link
 <!--
-If this pull request addresses a Help Wanted ticket, please link the relevant GitHub issue, e.g.
+If applicable, please include both or either of the following links:
 
-Fixes https://github.com/mattermost/mattermost-server/issues/XXXXX
-
-Otherwise, link the JIRA ticket.
+Fixes https://github.com/mattermost/mattermost/issues/XXX
+Jira https://mattermost.atlassian.net/browse/MM-XXX
 -->
 
 #### Related Pull Requests
 <!--
-List all PRs related to resolving a ticket. For instance, if you submitted a PR to `mattermost/mattermost-server`, please include it here.
+List all PRs related to resolving a ticket. For instance, if you submitted a PR to `mattermost/mattermost`, please include it here.
 -->
 - Has server changes (please link here)
 - Has mobile changes (please link here)