Support sending back max field length metadata in MySQL wire protocol

[fulghum]

The MySQL wire protocol includes metadata about a column's maximum length, which seems to come directly from the maximum display length set when defining a field (e.g. tinyint(1)). Some MySQL drivers expose this information and some applications rely on it (example of casting tinyint(1) to boolean values). Dolt does not seem to populate this metadata for any types currently.

Note that the maximum display lengths are deprecated in the latest version of MySQL and they don't prevent you from storing larger values in the field, but they are still used by some applications.