add GitHub Pull request template (.md) file (#12943)

* add GitHub issue template (.yaml) and Pull request template (.md) files

* final changes after reivew

* add example of PRT comment and remove checklist section

.github/new_pull_request.md

@@ -0,0 +1,16 @@
+### Problem Statement
+
+
+### Solution
+
+
+### Related Issues
+
+
+<!-- ### PRT test Cases example
+trigger: test-robottelo
+pytest: tests/foreman/ui/test_contenthost.py -k 'test_syspurpose_mismatched'
+-->
+<!--
+PRT usage reference link: https://github.com/SatelliteQE/robottelo/wiki/Robottelo-Pull-Request-Testing-(PRT)-Process#usage-examples
+-->