Docs: Updates Changelog for 6.6.0 (#21753)

* Docs: Adds backendSrv notice

* Update CHANGELOG.md

Co-Authored-By: Leonard Gram <leo@xlson.com>

* Docs: Updates notice placement

* Changelog: v6.6.0

Co-authored-by: Leonard Gram <leo@xlson.com>

CHANGELOG.md

-# 6.6.0 (unreleased)
+# 6.7.0 (unreleased)
+
+## Breaking changes
+
+### Notice about changes in backendSrv for plugin authors
+
+In our mission to migrate away from AngularJS to React we have removed all AngularJS dependencies in the core data retrieval service `backendSrv`.
+
+Removing the AngularJS dependencies in `backendSrv` has the unfortunate side effect of AngularJS digest no longer being triggered for any request made with `backendSrv`. Because of this, external plugins using `backendSrv` directly may suffer from strange behaviour in the UI.
+
+To remedy this issue, as a plugin author you need to trigger the digest after a direct call to `backendSrv`. 
+
+Example: 
+
+```js
+backendSrv.get(‘http://your.url/api’).then(result => {
+    this.result = result;
+    this.$scope.$digest();
+});
+```
+
+You can test your plugin with the `master` branch version of Grafana.
+
+# 6.6.0 (2020-01-27)
+  
+### Features / Enhancements
+* **CloudWatch**: Add DynamoDB Accelerator (DAX) metrics & dimensions. [#21644](https://github.com/grafana/grafana/pull/21644), [@kenju](https://github.com/kenju)
+* **CloudWatch**: Auto period snap to next higher period. [#21659](https://github.com/grafana/grafana/pull/21659), [@sunker](https://github.com/sunker)
+* **Template variables**: Add error for failed query variable on time range update. [#21731](https://github.com/grafana/grafana/pull/21731), [@tskarhed](https://github.com/tskarhed)
+* **XSS**: Sanitize column link. [#21735](https://github.com/grafana/grafana/pull/21735), [@tskarhed](https://github.com/tskarhed)
+
+### Bug Fixes
+* **Elasticsearch**: Fix adhoc variable filtering for logs query. [#21346](https://github.com/grafana/grafana/pull/21346), [@ceh](https://github.com/ceh)
+* **Explore**: Fix colors for log level when level value is capitalised. [#21646](https://github.com/grafana/grafana/pull/21646), [@ivanahuckova](https://github.com/ivanahuckova)
+* **Explore**: Fix context view in logs, where some rows may have been filtered out.. [#21729](https://github.com/grafana/grafana/pull/21729), [@aocenas](https://github.com/aocenas)
+* **Loki**: Fix Loki with repeated panels and interpolation for Explore. [#21685](https://github.com/grafana/grafana/pull/21685), [@ivanahuckova](https://github.com/ivanahuckova)
+* **SQLStore**: Fix PostgreSQL failure to create organisation for first time. [#21648](https://github.com/grafana/grafana/pull/21648), [@papagian](https://github.com/papagian)
 
 # 6.6.0-beta1 (2020-01-20)