Searches customers by name, mobile number or passport (passport only when the company's passport-scanning setting is enabled), as used by the POS customer picker. Exact matches are returned first, then partial matches (name contains the query, mobile/passport start with it), up to 20 results in total. The query must be at least 2 characters, otherwise the call fails with 400 BAD_REQUEST. Requires the p/r-customer permission.