feat: add CHANGELOG entry for container version bump to Python 3.8 / Ubuntu 20

Author: jstaph

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## In Development
 * Advanced Feature: Make securityContext (on Deployments/Jobs) and podSecurityContext (on Pods) configurable. This allows dropping all capabilities, for example. You can override the securityContext for `st2actionrunner`, `st2sensorcontainer`, and `st2client` if your actions or sensors need, for example, additional capabilites that the rest of StackStorm does not need. (#271) (by @cognifloyd)
 * Prefix template helpers with chart name and format helper comments as template comments. (#272) (by @cognifloyd)
+* Migrate from `python 3.6` `Ubuntu Bionic` to `python 3.8` `Ubuntu Focal` as a base StackStorm OS (StackStorm/st2-dockerfiles#54)
 
 ## v0.80.0
 * Switch st2 to `v3.6` as a new default stable version (#274)