add project.column.search api endpoint

[rebortg]

add the missing api endpoint "project.column.search" to the interfaces.json file. it is this part:

"project.column.search": {
    "description": "Search for Workboard columns.",
    "params": {
        "ids": "optional list<int>",
        "phids": "optional list<phid>",
        "projects": "optional list<phid>"
    },
    "return": "list"
},