DOC: Clarify interaction between defaultValue and populate

The populate property of the openDialogAction interacts with the defaultValue of select fields in non obvious ways: to apply the default value of a radio button group field, setting defaultValue alone is not sufficient and populate=false needs also be set on the corresponding open dialog action. I suggest we improve the documentation to that respect.

The documentation of defaultValue has the note "Applied only when creating a new item, not for already existing items", which could be related. No mention of the populate property though.

The documentation of OpenDialogActionDefinition mentions the populate property but stays very vague: "can trigger exceptions in some cases".

Note that I don't have the full picture on how and where the populate and defaultValue properties interact. Maybe @Roman Kovařík has more insight and can help with the details.

Note

This was discovered in the ABn testing app where setting the default value alone did not selected the "now" option until populate was set to false in the open dialog action.