[ANNOUNCE] Log4j module deprecation

In order to concentrate our limited resources on the remaining modules,
the PMC decided to deprecate the following modules/features in 2.x and
to remove them in 3.x:
 * `log4j-cassandra`,
 * CouchDB appender,
 * GELF appender,
 * Kafka appender,
 * jeroMQ appender,
 * `log4j-jpa`,
 * `log4j-mongodb3`,
 * `log4j-spring-boot`,
 * Java EE SMTP appender,
 * `log4j-taglib`.

Each of these modules either has a valid (and maintained) third-party
alternative or its usage has been deemed irrelevant.

Piotr