Port
cakephp/phinx#2360
to Migrations

Adds a new -k / --count option to the migrate command which allows for running arbitrary number of migrations, without relying on target or date. Decided to use the -k shorthand as -c, -n, and -t were already used, and it can stand for "kount" which I feel like other tools have done (vs -o as suggested in the issue, which feels more arbitrary).
I decided to deal with rollback in a follow-up PR as there's a workaround for this functionality there, which is just running the rollback command however many times you need.

I guess we dont need a shorthand even, count is short enough.

Refs also cakephp/phinx#2369