Add the ability to specify checkpoint properties to Agent library

[benedeki]

Background

Agent support of checkpoint properties

Feature

Enhance the method of AtumContext.createCheckpoint to accept a Map{String, String] parameter of the checkpoint properties. It defaults to an empty map.
Similarly change the DataDrame's implicit method of the same name.

The parameter is the sent into the new API endpoint.

Depends on #350

[benedeki]

This item depends on:

• Adjust API endpoints to accept and return checkpoint properties #350
  By Dependent Issues.