Gantt: Add support for callback with parameters

[keenanjt33]

This is meant to address: #921

After researching this issue I agreed with Dunning-Kruger that it seemed prudent to support passing in the node identifier as the callback parameter as a solution. I then found that the project already supports this for flowcharts. Gantt charts, on the other hand, already support passing in custom parameters to a callback function. This, however, was not reflected in the documentation.

For continuity between flowchart and Gantt, I added in code to automatically pass in the task identifier to the callback function if no custom callback parameters are specified. I also added interaction documentation based off of the documentation for flowchart and #804.

This would be my first contribution so any feedback would be appreciated.

[knsv]

@keenanjt33 Thanks Keenan! Great that you added docs and tests! We have a browser suite using cypress and it would be neat to have this change covered in the integration tests. If you add that I would be happy to merge this PR

Path:
cypress/integration/other/interaction.spec.js

to run, do yarn devto start the dev server. Then in another command prompt do cypress open.

[knsv]

@keenanjt33 Thanks Keenan! Great that you added docs and tests! We have a browser test suite using cypress and it would be neat to have this change covered in the integration tests. If you add that I would be happy to merge this PR

Path:
cypress/integration/other/interaction.spec.js

to run, do yarn devto start the dev server. Then in another command prompt do cypress open.