[Go] Support unsigned dictionary indices

[asfimport]

Reporter: Wes McKinney / @wesm
Assignee: Matthew Topol / @zeroshade

Related issues:

• [Format] Permit unsigned dictionary indices in Columnar.rst (is a child of)
• [Go] add support for DictionaryArray (is fixed by)

_{Note: This issue was originally created as ARROW-9378. Please see the migration documentation for further details.}