[5.0] Add auto incrementing id column to migrations

[alexwhitman]

As an alternative to #7244 this adds an auto incrementing id column to the migrations table. This gives the table a primary key but doesn't have any issues around string index length.

[ravanscafi]

Why should it be included? There's no relation between migrations and other tables.

[RomainLanz]

@rscafi Just look at the linked pull ;)

[taylorotwell]

We actually tried this once and it caused issues.

[alexwhitman]

@taylorotwell Adding an id column caused problems? Are you not getting mixed up with indexing the migration column which can cause issues?