[Integration][Documentation] Document JSON test data for BinaryView and Utf8View

[bkietz]

Describe the enhancement requested

JSON is used to represent integration data to enable independent validation of readers and writers. https://arrow.apache.org/docs/dev/format/Integration.html#json-test-data-format

#37526 adds generation of JSON for the new types but did not document it, which should be rectified

#37792 (comment)

Component(s)

Documentation, Integration