Introduce command-line tool to dump blocks as JSON

[abailly-iohk]

Description

This PR introduces a command-line utility to be able to dump some random CBOR encoded block content as a more human-readable JSON data structure. It can also extract an arbitrary block from a node's immutable DB and dump its content.

The motivation for this PR came when we were troubleshooting some incident on the network with @JaredCorduan @disassembler and others and realised we did not have any tool handy to read the raw content of a block.

Early feedback from Consensus experts:

• Is such a tool useful? ✅
• Perhaps there's something better somewhere to do that job that I am not aware of? ❌
• Does it make sense to put it there? ✅
• Is it missing some obvious feature? ❌

Known limitations:

• It's missing tests (I still need to understand how to generate blocks to write some property test),
• It's does not cover eras prior to Alonzo,
• It only reads from Immutable DB
• Its name is lame
  • probably ok for now, we can change it later
• Code format does not respect ouroboros-network's conventions

Checklist

• Branch
  • Commit sequence broadly makes sense
  • Commits have useful messages
  • The documentation has been properly updated
  • New tests are added if needed and existing tests are updated
  • Any changes affecting Consensus packages must have an entry in the appropriate changelog.d directory created using scriv. If in doubt, see the Consensus release process.
  • If this branch changes Network and has any consequences for downstream repositories or end users, said changes must be documented in interface-CHANGELOG.md
  • If serialization changes, user-facing consequences (e.g. replay from genesis) are confirmed to be intentional.
• Pull Request
  • Self-reviewed the diff
  • Useful pull request description at least containing the following information:
    • What does this PR change?
    • Why these changes were needed?
    • How does this affect downstream repositories and/or end-users?
    • Which ticket does this PR close (if any)? If it does, is it linked?
  • Reviewer requested

[dnadales]

Would it make sense to refer to the output of block-tool -h to avoid repeating the text here?

[abailly-iohk]

Sort of, yes. My goal here was more to convey a sense of what this tool looks like.

[abailly-iohk]

Thanks for your review @dnadales and the approval! However this is just a draft in order to get early feedback from experts, I don't plan to merge this PR as-is if only because it has no tests :) I will take your approval as a sign this effort is worthwhile to pursue.

[abailly-iohk]

Should I do something for this to be merged?

[dnadales]

Should I do something for this to be merged?

I'd say let's merge this, announce it to other teams, and document it in ouroboros-consensus

[abailly-iohk]

bors+