ListStores should support pagination

[yuryu]

ListStores should support pagination because it returns N results.

[hongalex]

We should add pagination options to ListStores, similar to Pub/Sub

Alternative considered was to make it streaming but streaming endpoints are harder to use than unary and is overkill for ListStores.

[yuryu]

Making ListStores pageable won't break compatibility, so I'll change the issue and remove the 1.0.0 tag.