Add TaskLauncher-Proxy application

[sabbyanandan]

As a continuation from https://github.com/spring-cloud/spring-cloud-dataflow/issues/3406, we would require a TaskLauncher-Proxy application, an ephemeral Task application that can be the proxy to invoke the desired Tasks when triggered by the Scheduler implementations.

Acceptance:

• Decide whether or not it will be an App Starter or a simple Task+Boot application
• The goal is to release this application in alignment with SCDF's 2.3 GA timeline, so it needs to be released standalone and not as part of the next release train
• See if there's an opportunity to reuse some core infrastructure from the tasklauncher-dataflow - perhaps move the common code to somewhere that can be shared?
• Tests included
• Docs/README included

[sabbyanandan]

Closing this in favor of https://github.com/spring-cloud/spring-cloud-dataflow/issues/3494.