R1:ad3745c80181

Add a "columns" attachment to the maniphest.search API method

Summary:
Ref T12074. This allows callers to identify which columns an object appears in (currently, always tasks).

There are a few major cases:

- Object is in a normal column: we return column information.
- Object is in a proxy column (subproject or milestone). For example, when you look at the board for "Some Parent Project", the task might show up in a milestone column. I've chosen to not return anything in this case: you can figure…