Make Upstream changes in gnodev to facilitate extension

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Review comments here gnolang/gno#4186

TODO: augment the gnodev build w/ feature flags to avoid duplicating the ./cmd in the gno repo.

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Still iterating on some features under the gnoserve codebase.
Once we have identified the features we wish to offer, will re-examine the upstream integration.

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added an MR to introduce an easier way to extend goldmark gnolang/gno#4400