Filter query by whether a property or properties exist

[dshanske]

This would filter a query by property names existing or not existing. Originally discussed in #4

exists[] - Matches one or more property names (for example, exists[]=like-of)
not-exists[] = Inverse of exists

[jalcine]

Shock implements this as a client. It's used to power the 'micro' feeds on my homepage. Also, Koype implements this as a server as of 2022-06-29.

(Originally published at: https://jacky.wtf/2022/7/axLD)