add docs and test for sameSite attribute in AdaptiveStorage

[makepanic]

#2312 added proxying of the attribute but did not add proper documentation and testing.

[makepanic]

From the issue comment:

adding the new property to the adaptive store and documenting it

I've copied the documentation from the cookie store sameSite jsdoc comment.

passing it to the cookie store

done

adding a test for that behavior (I know the adaptive store tests are a mess – if you need help with that, let me know)

I've extended the existing cookie attribute related adaptive test.
I could also add a new test for this one case as the existing one might have a different focus.