Id: Add checkbox option to tag eateries as vegetarian/vegan

[nicolasmaia]

The keys diet:vegetarian and diet:vegan allow three values: yes, no and only. Here are some more details:

• https://wiki.openstreetmap.org/wiki/Key:diet:vegetarian
• https://wiki.openstreetmap.org/wiki/Key:diet:vegan

This is particularly helpful to avoid the spread of cuisine=vegetarian/vegan, which is deprecated.

[bhousel]

I could see adding multicombo field for diet: as a moreField (recently added in #5582) .
I definitely don't want to add checkboxes for every kind of diet: that people think of.

[bhousel]

I could see adding multicombo field for diet: as a moreField

☝️ I did this