[5.5] Adding SameSite to config/sessions

[fernandobandeira]

This allow us to specify a default value for this option on the sessions config file...

We could rename the methods setDefaultPathAndDomain and getPathAndDomain to something else like setDefaultOptions and getDefaultOptions would it be a good idea?

[sisve]

Renaming the methods would be a breaking change; couldn't you just create two new methods; getSameSite and setSameSite?

[fernandobandeira]

Yes I could, but it's already being used for secure too so it already doesn't make that much sense...

[taylorotwell]

Change this to same_site since we always use snake_case in config and also defaulted it to null in several places.