Add "project.column.search" for querying workboard column information

Summary:
Ref T12074. Provide a basic but functional v3 API endpoint for reading workboard column information.

There is no equivalent to this in the UI yet, although there may be some day (perhaps adjacent to T5024).

Test Plan:

• Queried for all columns.
• Queried for columns on a particular board using projectPHIDs.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12074

Differential Revision: https://secure.phabricator.com/D17157