[fenix] Create --unit-test.md

.github/ISSUE_TEMPLATE/--unit-test.md

@@ -0,0 +1,13 @@
+---
+name: "\U0001F6A8 Intermittent Unit Test Issue"
+about: Create an issue to help log a Unit Test failure
+labels: "eng:intermittent-test"
+title: "Intermittent Unit Test failure - <Classname.testName>"
+assignees: ''
+
+---
+
+### Test Run:
+Provide a test run report link here showcasing the problem (e.g, Taskcluster), and a link to the source Github event
+### Stacktrace:
+### Build: