The cosmos-sdk 0.50 genesis doc marshalling not being compatible with
the cometbft default one (see
cosmos/cosmos-sdk#18477), so we need to
support custom genesis doc provider in this public API as well, it's
called by the `bootstrap-state` command in cosmos-sdk.

Please backport to 0.38, the SDK 0.50 `bootstrap-state` command is
already broken.

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---

#### PR checklist

- [ ] Tests written/updated
- [ ] Changelog entry added in `.changelog` (we use
[unclog](https://github.com/informalsystems/unclog) to manage our
changelog)
- [ ] Updated relevant documentation (`docs/` or `spec/`) and code
comments
- [ ] Title follows the [Conventional
Commits](https://www.conventionalcommits.org/en/v1.0.0/) spec

(cherry picked from commit 7279fe8)