[BUGFIX] Add default values to text fields

[mschwemer]

Since mysql 8.0.13 and mariadb 10.2.1 NOT NULL without a defined default value are not allowed any more. Adding a default value solves the issue.

Fixes: #229

[bobosch]

Mysql does not allow default values on text fileds :-(

https://dev.mysql.com/doc/refman/9.7/en/blob.html
"BLOB and TEXT columns cannot have DEFAULT values."

[mschwemer]

Hmmm ...

ext_tables.sql is SQL pseudo code, which is parsed via doctrine dbal and not a mysql native sql code. Prior to mysql 8.0.13 the default part is stripped off https://github.com/doctrine/dbal/blob/1a2fbd0e/src/Platforms/MySQLPlatform.php#L28-L34.

With mysql 8.0.13 it is possible to provide default values for TEXT fields: https://dev.mysql.com/doc/refman/8.0/en/data-type-defaults.html#data-type-defaults-explicit-old ... 3rd paragraph:

The BLOB, TEXT, GEOMETRY, and JSON data types can be assigned a default value only if the value is written as an expression, even if the expression value is a literal.

I would update the PR using an expression for the default value, if you like.

[bobosch]

Also all sysext have no DEFAULT on text and blob fields ...