Possible to preserve previous data when manual=true

[andyvanhelsing]

Hi there I am new to react-query and I was wondering if there is a built in method to preserve the last data response when a query key changes while in manual mode? Ideally I would like to save the previous results until refetch is called (or use the last data value as initialData). Thanks so much for all your work on this project!

[cherniavskii]

See #419