post https://dialpad.com/api/v2/numbers//assign
Assigns a number to a target. Target includes user, department, office, room, callcenter,
callrouter, staffgroup, channel and coachinggroup. The number will automatically be taken from the company's reserved pool if there are reserved numbers, otherwise a number will be auto-assigned from the provided area code.
Added on May 26, 2020 for API v2.
Rate limit: 1200 per minute.