Apply GitHub default community health

* Remove `CODE_OF_CONDUCT.adoc` if favor of the same for a GitHub org
* Move `LICENSE.txt` to the root project dir
* Fix `build.gradle` to copy a `LICENSE.txt` from the actual location
* Fix `README.md` and `CONTRIBUTING.adoc` to point into the actual `CODE_OF_CONDUCT`
& Security policy
* Add `ISSUE_TEMPLATE` directory with files similar to ones in `spring-session`
* Fix wrong section `id` in the `whats-new.adoc`

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,25 @@
+---
+name: Feature request
+about: Suggest an idea for this project
+title: ''
+labels: 'status: waiting-for-triage, type: enhancement'
+assignees: ''
+
+---
+
+**Expected Behavior**
+
+<!--- Tell us how it should work -->
+
+**Current Behavior**
+
+<!--- Explain the difference from current behavior -->
+
+**Context**
+
+<!--- 
+How has this issue affected you?
+What are you trying to accomplish?
+What other alternatives have you considered?
+Are you aware of any workarounds?
+-->