Add the diff option for the runtime_config endpoint

[ethervoid]

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The new runtime_config endpoint could be a little verbose and hard to read because is returning all the defaults values

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We need to add a new diff option, like the config endpoint, to just show the changed values and discard the defaults values

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This comes from #1324

[ethervoid]

@pracucci I've added this issue as requested, I'd like to keep working on it, could you assign it to me please?