[3442] add MultipleSocketAppender

[lu-xiaoshuang]

#3442

[vy]

@lu-xiaoshuang, as @ppkarwasz stated in #3442

1. Create and publish a new appender (let's say MultiSocketAppender) in your personal or company repo under Apache-2.0.

We recommend you to publish this plugin (under Apache 2.0 license) in your personal or your employer's GitHub account. For instance, see my Redis Appender or @ppkarwasz's Tomcat plugin.

[ppkarwasz]

We recommend you to publish this plugin (under Apache 2.0 license) in your personal or your employer's GitHub account.

Once you have done a release, let us know, so we can advertise it on our website.

[ppkarwasz]

Once you have done a release, let us know, so we can advertise it on our website.

See #3534 for an example PR on how to add a reference to your appender to our documentation website.