Move querying scheduled rewards to individual modules

[bajtos]

See the discussion in #259:

It's the module's decision whether to use Meridian. ethers might even run in Zinnia, since for this we don't need to sign messages - or we could just use the jsonrpc endpoint directly - then we only need fetch. I think for this we need a way for Zinnia modules to log metrics.

Tasks

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1. Allow modules to report scheduled rewards zinnia#421
   feature good first issue 🤗 +2
2. Release new Zinnia version and bring it to Station Core
3. Update SPARK to use this new API
4. Release new SPARK version and bring it to Station Core
5. Rework Station Core to use this new metric provided by zinniad

[bajtos]

@juliangruber is this something we should consider for the DARC workstream or are you ok to duplicate the current code in Station Core to query scheduled rewards for another module?

[juliangruber]

Good question, let's decide as we work on the implementation