[sftp-dataflow-source] Add support to launch Tasks dynamically

[sabbyanandan]

As a user, I'd like to have the option to dynamically launch tasks in DataFlowTaskLaunchRequest, so I can assign a different "task name" for each of the consumed SFTP payloads.

Notes:

• This requires changes to RotatingServerAdvice and StandardRotationPolicy in SI to extend it in sftp-dataflow to then add support for it.
• Once that is added to SI, we will inherit the upstream changes to redesign the sftp-dataflow application to optionally also configure and pin each payload to a particular Task.

[dturanski]

Currently on hold until we upgrade app starters to Spring and SI 5.2 since the required SI change is considered a breaking change for SI 5.1. spring-projects/spring-integration#3028 (comment)