Add flexible configuration option that allows to ignore legacy migrations

[waterlink]

fixes #10
related to #11

/cc @anthonyalberto

[anthonyalberto]

Cool! Thanks for the contribution, really appreciated

I'm trying to think if a proc is really required here though. I can't see when it would be a good idea to ignore when version is greater of a given value for example.

What about just having a setting : config.active_record.mysql_online_migrations_min_version and if the value is stricly less than that, we just skip it.

Easier to configure and I think that covers the only use case I can think of

What do you think?

[waterlink]

@anthonyalberto in most cases you don't need block.

But I have a project with multiple databases, where we have two independent migration sets with different versioning semantics, i.e.

20120508133018_ vs 017_

The only feasible way to do this for me is to use block

[waterlink]

@anthonyalberto Hi, any news on this one, WDYT, is there any compromise to make it a very simple configuration option, but still leave a possibility to provide a custom ignoring mechanics?

[waterlink]

How about having both mysql_online_migrations_ignore_before = "20120508133018" and mysql_online_migrations_ignore = -> (version) { ... custom logic here ... }

WDYT?