Configurable worker thread join timeout in AsyncAppenderBase

AsncyAppenderBase currently only waits 1000ms for the worker thread to finish processing. For some higher latency appenders, such as cloud logging services, this timeout on the join call may not be sufficient. With this change, the end user can configure the timeout with the same semantics as Thread.join (including use '0' to wait indefinitely).


Updated AsyncAppenderBase to have a configurable worker thread join timeout instead of the default 1000ms. Added unit test to verify correct function and updated appenders documentation describing new configuration parameter and suggested uses. Added to news page under release 1.1.3.