Add ADR for using Cider to manage changelog

(cherry picked from commit 2edfa6ce39989b5d3c441815ddd1d6fd8e376eb4)

docs/adr/0021-manage-changelog-by-cider.md

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+# 21. Manage Changelog by Cider
+
+Date: 2023-04-05
+
+## Status
+
+Accepted
+
+## Context
+
+- We did not manage Changedlog with the standard way
+
+## Decision
+
+Use Cider (https://pub.dev/packages/cider) to easier to manage changelog to follow [Changelog](https://keepachangelog.com/en/1.1.0/) format 
+
+## Consequences
+
+- We should add to the change log some `type` of change: `added`, `changed`, `deprecated`, `removed`, `fixed`, `security` in each PR with command
+```
+cider log <type> <description>
+```
+
+- In release phase, change the version in `pubspec.yaml` and dont forget to change the tag in cider template in the same file
+
+- Then run:
+```
+cider release
+```