Conway genesis DRep injection

[Soupstraw]

Description

This PR adds cgDRepDelegs and cgInitialDReps fields to ConwayGenesis so the benchmark team can inject DReps and DRep delegations into the state.

The actual injection is done via registerDRepDelegs and registerInitialDReps, which are exported in the API.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated
• When applicable, versions are updated in .cabal and CHANGELOG.md files according to the
  versioning process.
• The version bounds in .cabal files for all affected packages are updated. If you change the bounds in a cabal file, that package itself must have a version increase. (See RELEASING.md)
• All visible changes are prepended to the latest section of a CHANGELOG.md for the affected packages. New section is never added with the code changes. (See RELEASING.md)
• Code is formatted with fourmolu (use scripts/fourmolize.sh)
• Cabal files are formatted (use scripts/cabal-format.sh)
• hie.yaml has been updated (use scripts/gen-hie.sh)
• Self-reviewed the diff

[lehins]

Addition of new fields looks good for the most part. Injection is totally wrong. Please, let me know if you get stuck or if my comments are not clear enough.

[lehins]

Looks great. Thank you!