New changelog scripts (#4491)

* Add templates

* Add folder for local storage of the digests

* Add first draft of the changelog scripts

* Enable Audits in the change template

* Fixes for Polkadot

* Fix templating issue in case there is no high prio change

* Fix Ruby setup

* Remove shell

* Fix chain names

* Fix ENV

* Fix how to get runtime

* Fix runtime_dir

* Fix context location

* Pin changelogerator to a specific version

polkadot/scripts/changelog/templates/changes.md.tera

@@ -0,0 +1,13 @@
+{# This include generates the section showing the changes #}
+## Changes
+
+### Legend
+
+- {{ DOT }} Polkadot
+- {{ SUB }} Substrate
+
+{% include "changes_client.md.tera" %}
+
+{% include "changes_runtime.md.tera" %}
+
+{% include "changes_misc.md.tera" %}