Mention EOL Elasticsearch 6.6 in 3.x release notes

Initialize notes with this for the next Gerrit 3.0 and 3.1 minor
releases. For the next Gerrit 3.2 minor release, add this to the already
initiated notes.

Change-Id: I262dc4aa21bb39d3bc9a6dde5adaee3814cf20b9
diff --git a/pages/site/releases/3.0.md b/pages/site/releases/3.0.md
index 6a78cb9..6accc04 100644
--- a/pages/site/releases/3.0.md
+++ b/pages/site/releases/3.0.md
@@ -210,6 +210,12 @@
 
 ## Bugfix Releases
 
+### 3.0.13 (in development)
+
+* Breaking Changes
+
+  * Elasticsearch: Support for EOL version 6.6 is discontinued.
+
 ### 3.0.12
 
 * Security Fixes
diff --git a/pages/site/releases/3.1.md b/pages/site/releases/3.1.md
index 97bd321..f198a72 100644
--- a/pages/site/releases/3.1.md
+++ b/pages/site/releases/3.1.md
@@ -306,6 +306,12 @@
 
 ## Bugfix Releases
 
+### 3.1.9 (in development)
+
+* Breaking Changes
+
+  * Elasticsearch: Support for EOL version 6.6 is discontinued.
+
 ### 3.1.8
 
 * Security Fixes
diff --git a/pages/site/releases/3.2.md b/pages/site/releases/3.2.md
index dd397a9..9522471 100644
--- a/pages/site/releases/3.2.md
+++ b/pages/site/releases/3.2.md
@@ -595,6 +595,10 @@
 
 ### 3.2.4 (in development)
 
+* Breaking Changes
+
+  * Elasticsearch: Support for EOL version 6.6 is discontinued.
+
 * Security Fixes
 
 * Bug Fixes