MariaDB source doesnt extract JSON columns properly [DBZ-9430]

Migrated from [DBZ-9430](https://issues.redhat.com/browse/DBZ-9430)

Mariadb stores JSON as LONGTEXT, not JSON. So, when you have a JSON column in mariadb, it just comes out with a string in the schema, rather than io.debezium.data.Json

 
{code:java}
{    
"name": "json_col",
"type": ["null","string"],
"default": null
}{code}
Here's a blog post from Mariadb on the topic
[Making MariaDB understand MySQL JSON - MariaDB.org|https://mariadb.org/making-mariadb-understand-mysql-json/]

And from their docs;:

{{JSON}} is an alias for {{{}LONGTEXT{}}}. See [JSON Data Type|https://mariadb.com/docs/server/reference/data-types/string-data-types/json] for details.

In MySQL, JSON is an object and is [compared according to json values|https://dev.mysql.com/doc/refman/8.0/en/json.html#json-comparison]. In MariaDB JSON strings are normal strings and compared as strings. One exception is when using [JSON_EXTRACT()|https://mariadb.com/docs/server/reference/sql-functions/special-functions/json-functions/json_extract] in which case strings are unescaped before comparison. 

So, Its really just a LONGTEXT. 

I think that all that could probably be done is change the docs [Debezium connector for MariaDB :: Debezium Documentation |https://debezium.io/documentation/reference/3.2/connectors/mariadb.html#mariadb-basic-types]to say that JSON is actually LONGTEXT and will output as string, and wont have io.debezium.data.Json