Support custom charset and collation for schema_migrations table (mysql)

[mheffner]

For MySQL the default schema_migrations table is created using a latin1 charset and latin1_bin collation:

> show create table schema_migrations;
+-------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table             | Create Table                                                                                                                                              |
+-------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+
| schema_migrations | CREATE TABLE `schema_migrations` (
  `version` varchar(255) NOT NULL,
  PRIMARY KEY (`version`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_bin |
+-------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------+

This is incompatible with some database providers, like Planetscale. Planetscale requires a utf8 charset/collation.

It looks like this is hardcoded here. It would be great if this were configurable.

[amacneil]

Some history on this:

• On MySQL 5.6 with default utf8mb4 encoding, schema_migrations table fails to create #85
• Create the schema_migrations table using latin1 charset in MySQL #172

Potential solutions:

• Change the version varchar length to 128 and remove the explicit charset
• Make it configurable (how)

Thoughts? I'm leaning towards the first option.

[mheffner]

Thanks for the context! Yes, the first option makes the most sense IMO given your comment also mentions that these fields are usually only 14 chars long.

[amacneil]

PR: #391