Replace issue templates with links to jenkins.io (#956)

Author: KalleOlaviNiemitalo

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,11 @@
+blank_issues_enabled: false
+contact_links:
+  - name: Report an issue to JIRA
+    url: https://www.jenkins.io/participate/report-issue/redirect/#21428
+    about: Please report new issues of this plugin to JIRA, not to GitHub.
+  - name: View open issues in JIRA
+    url: https://issues.jenkins.io/issues/?jql=resolution%20is%20EMPTY%20and%20component%3D21428
+    about: View the open issues of this plugin at issues.jenkins.io.
+  - name: Issue tracking policy
+    url: https://github.com/jenkinsci/bitbucket-branch-source-plugin/blob/master/README.md#issue-tracking-where-file-new-issues
+    about: Existing issues in GitHub will be migrated to JIRA.