@morozov review: According to MySqlPlatform::getListTableColumnsSQL(), the default column is always selected. Removed ??

#2815 don't require `ssl_key` and `ssl_cert` to use `ssl_ca`

Fixes: https://github.com/doctrine/dbal/issues/2815

Fixes custom type comment regex

Fixes: https://github.com/doctrine/dbal/issues/2596
Replaces: https://github.com/doctrine/dbal/pull/2679

Don't Set a Default Value on PostgreSQL SERIAL Fields

Fixes: https://github.com/doctrine/dbal/issues/2906

Serial fields already have a default value. By opting out of `notnull`
serial fields will just set the next value in the sequence.

Postgres has a `SERIAL` data type to allow shorthand for
`nextval('sequence_name')`, but DDL like this:

    CREATE TABLE example (id SERIAL)

Cannot be generated in the DBAL schema APIs.

Default value declaration for immutable types

Fixes: https://github.com/doctrine/dbal/issues/2859