Adjust Readyset Protocol::ColumnDefinition41

[altmannmarcelo]

Description

https://dev.mysql.com/doc/dev/mysql-server/latest/page_protocol_com_query_response_text_resultset_column_definition.html

Our protocol definition for below items differ from MySQL:

• character_set
• column_length
• decimals
• flags (out of the scope)

We should fix the first 3 items

Change in user-visible behavior

Requires documentation change