misc(github): add issue template (spark-jobserver#935)

Author: derSascha

.github/issue_template.md

@@ -0,0 +1,22 @@
+**Used Spark version**
+
+**Used Spark Job Server version**
+(Released version, git branch or docker image version)
+
+**Deployed mode**
+(client/cluster on Spark Standalone/YARN/Mesos/EMR or default)
+
+**Actual (wrong) behavior**
+
+**Steps to reproduce**
+
+**Logs**
+
+```
+some log
+```
+
+or as attached file (see below)
+
+
+Unused parts of this template should be removed (including this line).