[remote_config] Default Values

[fabricio-godoi]

After I checked out the newest release, I got a little concerned with the approach used in the setDefaults in the PR #6817.

It seems that the issues related to this PR is about some quotes being striped from the string and not being able to serialize and deserialize the data properly (#2074 and #6074). When reading the issues, I got to the point where I found that the issue could occur in the native side of the platforms, since it seems to be returning some unknown map from the function getString.

The problem with the approach suggested in #6817 is that it is not fully compatible with the way that RemoteConfig allows the users to store its data (JSON format). Since only primitives values are allowed, something like {"foo": {"bar": "low"}} are not allowed in the defaultConfig, since store an object. Also, the project does not clearly mention that it is not possible to store the object in the localhost defaultConfig, which will increase the issues on that matter.

I strongly suggest a review of this approach to find where in the code is the real problem, instead of trying to force it to work with that workaround.