Fix accidental removal of changelog entry

During a rebase the latest 4 series entry was deleted. This restores it.

Author: donoghuc

CHANGELOG.md

@@ -1,11 +1,14 @@
-## 5.0.0 ##
+## 5.0.0
  - SSL settings that were marked deprecated in version `4.17.0` are now marked obsolete, and will prevent the plugin from starting.
  - These settings are:
  - `ssl`, which should bre replaced by `ssl_enabled`
  - `ca_file`, which should bre replaced by `ssl_certificate_authorities`
  - `ssl_certificate_verification`, which should bre replaced by `ssl_verification_mode`
  - [#213](https://github.com/logstash-plugins/logstash-input-elasticsearch/pull/213)
 
+## 4.20.5
+ - Add `x-elastic-product-origin` header to Elasticsearch requests [#211](https://github.com/logstash-plugins/logstash-input-elasticsearch/pull/211)
+
 ## 4.20.4
  - Fix issue where the `index` parameter was being ignored when using `response_type => aggregations` [#209](https://github.com/logstash-plugins/logstash-input-elasticsearch/pull/209)