Support separate path for sql migration files

[mohammadVatandoost]

Currently, all migration files must be in the same directory. I want to a feature that gives us ability to put migration sql files in separate directories.

As you see in following code, we can just add a fs to source.Driver. func New(fsys fs.FS, path string) (source.Driver, error)

It will be nice, if we can pass multiple fs to source.Driver, like this: func New(fsys []fs.FS, path string) (source.Driver, error)

[mohammadVatandoost]

I would like to work on this feature. If it is ok, please assignee to me.