Introduce Docker Packaging changelogs (#856)

* Enable Release Drafter to track changelogs in packaging versions

* GitHub Releases: Add clarification of the changelog process and versioning scheme to CHANGELOG.md

* Release Drafter: Link the upstream documentation

* Release Drafter: Add an "experimental" disclaimer to changelog drafts

* Reference the dev list discussion in README

* Reflect the LTS release tags and the versioning approach

* Release Drafter: Fix the name temlate

* Adjust Changelog information for the Release drafter

* Update CHANGELOG.md

Co-Authored-By: Daniel Beck <1831569+daniel-beck@users.noreply.github.com>

* Update CHANGELOG.md

* Update the Release Drafter pattern to match the manually generated changelog

* Fix typo

.github/release-drafter.yml

@@ -0,0 +1,15 @@
+# https://github.com/jenkinsci/.github/blob/master/.github/release-drafter.adoc
+_extends: .github
+# We are using 3-digit LTS versioning here
+version-template: $MAJOR.$MINOR.$PATCH
+tag-template: jenkins-docker-packaging-$NEXT_PATCH_VERSION
+name-template: Jenkins Docker Image $NEXT_PATCH_VERSION
+template: |
+  <!-- Optional: add a release summary here -->
+  ## 📦 Jenkins Core updates  
+  
+  * Update to Jenkins $NEXT_PATCH_VERSION ([changelog](https://jenkins.io/changelog-stable/#v$NEXT_PATCH_VERSION)) 
+  
+  $CHANGES
+  
+  **NOTE:** This is an experimental changelog. See [this page](https://github.com/jenkinsci/docker/blob/master/CHANGELOG.md) for more info

CHANGELOG.md

@@ -1,6 +1,31 @@
 CHANGELOG
 =========
 
-2.99
------
+| See [GitHub releases](https://github.com/jenkinsci/docker/releases) |
+| --- |
+
+## Status
+
+We are doing experimental changelogs for Jenkins master Docker packaging
+([discussion in the developer list](https://groups.google.com/forum/#!topic/jenkinsci-dev/KvV_UjU02gE)). 
+This release notes represent changes in in the packaging, but not in the bundled WAR files. 
+Please refer to https://jenkins.io/changelog/ and https://jenkins.io/changelog-stable/ for WAR file changelogs.
+
+## Version scheme
+
+The repository follows the 3-digit scheme of [Jenkins LTS releases](https://jenkins.io/download/lts/).
+
+## Mapping of Docker packaging to Jenkins releases
+
+Both Weekly and LTS distributions follow the Continuous Delivery approach and pick up the most recent versions available by the time of the release Pipeline execution.
+In this repository we follow the Jenkins LTS releases and release packaging changelogs for them.
+There is no version mapping for Weekly releases, users should be using changelogs to track down the changes
+(see also [Issue #865](https://github.com/jenkinsci/docker/issues/865)).
+
+## Notable changes in Jenkins versions before 2.164.1
+
+Below you can find incomplete list of changes in Docker packaging for Jenkins releases
+
+### 2.99
+
 *  `/bin/tini` has been relocated to `/sbin/tini`, location defined by alpine