Add migration for common seo fields

[piotrpog]

I was thinking about making seomate easier to use when starting new project.

How about adding migration for some common seo fields - like description, seo image and robots? I usually group these fields within matrix field that has max and min limit set to 1.

There could also be migratiln for global with page-wide seo settings.

Such migration would not be mandatory, but it would be usefull to have such thing.

[mmikkel]

Hi @piotrpog, thanks for contributing!

I feel like SEOMate shipping with content migrations would be require one too many assumptions on our part, so this is probably not going to happen.