Add 2.11.11 changelog and bump VERSION

Author: N-o-X

CHANGELOG.md

@@ -7,6 +7,19 @@ documentation before upgrading to a new release.
 
 Released closed milestones can be found on [GitHub](https://github.com/Icinga/icinga2/milestones?state=closed).
 
+## 2.11.11 (2021-08-19)
+
+The main focus of these versions is a security vulnerability in the TLS certificate verification of our metrics writers ElasticsearchWriter, GelfWriter and InfluxdbWriter.
+
+### Security
+
+* Add TLS server certificate validation to ElasticsearchWriter, GelfWriter and InfluxdbWriter
+
+Depending on your setup, manual intervention beyond installing the new versions
+may be required, so please read the more detailed information in the
+[release blog post](https://icinga.com/blog/2021/08/19/icinga-2-13-1-security-release//)
+carefully
+
 ## 2.11.10 (2021-07-15)
 
 Version 2.11.10 fixes two security vulnerabilities that may lead to privilege

VERSION

@@ -1,2 +1,2 @@
-Version: 2.11.10
+Version: 2.11.11
 Revision: 1