Change event message schemas should have field metadata

Kafka Connect uses Schema objects to describe the key structure and value structure of each message. Each Schema defines each field within the corresponding Struct objects, and the fields define the field name, the type of value, whether the field is optional, and zero or more named string parameters.

The MySQL connector should add to fields for fixed-length types (e.g., CHAR, NCHAR, BIT arrays, etc.) a length parameter and for variable-length types (e.g., VARCHAR, etc.) a maxLength parameter. Additionally, any column mappings applied to the fields should be able to add parameters as well. For example, when a column is truncated or masked (see DBZ-29), then the field should have parameters that describe that it is masked, or update the maxLength or length parameters if the value in the field is truncated.