Make encoding.codec non-optional or default to json/ndjson

[binarylogic]

#1915 accidentally made encoding.codec non-optional in sinks and defaulting to "text. If we are going to default, the value should be "json" (or "ndjson"), otherwise, the user should be required to provide the option and choose. We made the option explicit so that the user is not surprised with the format, although, I think JSON is what most users would expect if it's supported.

My vote is to default to json/nsjdon when possible, otherwise, require the option.