Expose querySPOStakeDistribution query

[palas]

Changelog

- description: |
    Exposed `querySPOStakeDistribution` query
  type:
  - feature        # introduces a new feature

Context

We want to provide a governance query for stake distribution of stake pools to the cardano-cli (see this issue), so we need to be able to do the query through the cardano-api. This PR does just that, it exposes the new query.

Associated PRs:

• In cardano-cli: Implement query spo-stake-distribution cardano-cli#854
• In cardano-node: Add test for query spo-stake-distribution cardano-node#5932

How to trust this PR

I think the fact that it compiles is pretty telling. But maybe ensure that there is nothing missing to export, that it doesn't have any typos or so. And it is is quite based on the similar query for drepss, so it is not difficult that I failed to change replace some of the DRep mentions, stay alert for those (I did double-check myself though).

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff

[Jimbo4350]

LGTM! Be sure to test this on cardano-node before merging please.