Support bytes as a data type

[acmiyaguchi]

There's some use of the bytes SQL type for storing arbitrary binary data. bytes are generally not well formed in JSON, but supported in Avro and BigQuery. A low-impact solution is to create a custom bytes format under the string type, as follows:

{
  "type": "string",
  "format": "bytes"
}

This schema isn't used to validate the payload because documents containing binary data may also contain control characters that invalidate the JSON documents. Instead, the schema is descriptive and used to generate Avro/BigQuery schemas instead.

See: https://json-schema.org/understanding-json-schema/reference/string.html#format https://cloud.google.com/bigquery/docs/reference/standard-sql/data-types#bytes-type

[relud]

This schema isn't used to validate the payload because documents containing binary data may also contain control characters that invalidate the JSON documents

in json it should be encoded as a base64 string.

that said, we don't actually validate anything using this format, for now.