Added changelog file

Author: jesmith17

src/changelog/.3.x.x/update_org_log4j_mongodb.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="updated">
+  <issue id="3321" link="https://github.com/apache/logging-log4j2/pull/3321"/>
+  <description format="asciidoc">Update log4j-mongodb to allow collectionName and databaseName to be defined via the config file</description>
+</entry>