Ledger workers

[thibault-martinez]

Change checklist

Tick the boxes that are relevant to your changes, and delete any items that are not.

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked that new and existing unit tests pass locally with my changes
• I have updated the CHANGELOG.md, if my changes are significant enough

[Alex6323]

Are we in a hurry with this? Because otherwise I would wait until we merged the pruning logic to cpt2, and include it in this PR? It's not quite a small addition to bee-ledger invalidating a few files in this PR already. And if this gets merged to dev and therefore removed from cpt2 it will make things more difficult for me. Wdyt?