Add issue template

This commits adds an issue template for contributors that open bug
reports or feature requests.

Additionally, this commit adds a .github subdirectory to the project and
moves the CONTRIBUTING.md file to that directory.

Closes #16773

.github/ISSUE_TEMPLATE.md

@@ -0,0 +1,34 @@
+<!--
+GitHub is reserved for bug reports and feature requests. The best place
+to ask a general question is at the Elastic Discourse forums at
+https://discuss.elastic.co. If you are in fact posting a bug report or
+a feature request, please include one and only one of the below blocks
+in your new issue.
+-->
+
+<!--
+If you are filing a bug report, please remove the below feature
+request block and provide responses for all of the below items.
+-->
+
+**Elasticsearch version**:
+
+**JVM version**:
+
+**OS version**:
+
+**Description of the problem including expected versus actual behavior**:
+
+**Steps to reproduce**:
+ 1.
+ 2.
+ 3.
+
+**Provide logs (if relevant)**:
+
+<!--
+If you are filing a feature request, please remove the above bug
+report block and provide responses for all of the below items.
+-->
+
+**Describe the feature**: