Rename channel parameter help to hint

Help or hint texts can be provided to users of the CMS / Channel Manager. For example the document type hints, with an explanatory text per field. Also Channel parameters can be given an explanation text. There they are called 'help' texts. Soon we get Component properties help texts (CMS-7662) where they are called 'hints' also.

To align all the different ways to provide these texts I propose to rename the 'help'. for the Channel properties also to 'hint'.

This requires an update instruction for developers to rename all properties that have the ".help" suffix in channel properties descriptions to ".hint". And in the Channel Manager code the changes are minimal. Start at /hippo-addon-channel-manager/frontend-ng/src/app/channel/menu/channel/settings/propertyField/propertyField.controller.js