Add a generic parameter so TS users can use `serialize: false`

[pzuraq]

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Fixes #465, this has been the pattern I've generally seen for passing down generics like this. It is an unfortunate amount of boilerplate, but the type-safety you get with it is usually worth it (e.g. being able to constrain the other values of the config, in this case).

[apollo-cla]

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[kdsbatra]

Do we think we can merge this soon?

I am in process of making another Pull Request to work with latest MMKVStorageWrappers and would like to merge this first