[Go] Read and write 64-bit integers as strings in integration test JSON format

[asfimport]

Reporter: Wes McKinney / @wesm

Related issues:

• [Developer] Tracking issue: use strings for 64-bit int64 and uint64 in integration test JSON format (is a child of)
• [C++][Integration] Regression to /u?int64/ as JSON::number (is fixed by)
• [Go][Integration] Represent 64 bit integers as JSON::string (is duplicated by)

_{Note: This issue was originally created as ARROW-6517. Please see the migration documentation for further details.}