Fields should indicate that related conditional tags are present

A proper opening_hours field has eluded us for years (#974), not to mention a UI for conditional restrictions that would presumably be based on it (#2906). Meanwhile, there are plenty of features that have both a key and the conditional variant of that key set simultaneously, for example, maxweight=* and maxweight:conditional=*. At the very least, an unobtrusive label could appear at the bottom of a field to indicate that conditional tagging is present and can be edited using the raw tag editor.