Added Dijkstra era

[Soupstraw]

Description

This PR sets up a subproject for the new Dijkstra era

close #4955

Checklist

• Commits in meaningful sequence and with useful messages.
• Tests added or updated when needed.
• CHANGELOG.md files updated for packages with externally visible changes.
  NOTE: New section is never added with the code changes. (See RELEASING.md).
• Versions updated in .cabal and CHANGELOG.md files when necessary, according to the
  versioning process.
• Version bounds in .cabal files updated when necessary.
  NOTE: If bounds change in a cabal file, that package itself must have a version increase. (See RELEASING.md).
• Code formatted (use scripts/fourmolize.sh).
• Cabal files formatted (use scripts/cabal-format.sh).
• CDDL files are up to date (use scripts/gen-cddl.sh)
• hie.yaml updated (use scripts/gen-hie.sh).
• Self-reviewed the diff.

[Soupstraw]

I think it's fine to put the project directly into eras/dijkstra, since we don't want to have the cardano-ledger-<era>-test packages anymore. This gives us a shorter path to Dijkstra 😉

[lehins]

Yes, that is fine, especially since that is the ultimate goal for all of the previous eras. 👍

[lehins]

That is not what I had in mind when I created a ticket.

We need an era that is equivalent to Conway, not just a placeholder package.

In other words it should reuse all of the types and rules and should be running all of the reusable tests from previous eras, including impspec

[lehins]

@Soupstraw While performing this task I would like for you to also write up a document that explains the steps that are necessary to follow in order to define a new blank era that matches the behavior of the previous one exactly and executes all of the same tests.