Enhance end to end test for Cardano hard forks

[jpraynaud]

Why

We want the CI to test multiple scenario when a hard fork is planned on the Cardano chain, and in particular make sure that there is no problem in terms of communication between the Mithril and Cardano nodes.

What

The end to end test should be fully functional with the current versions of the Cardano node 8.1.2 and 8.7.3. We also want to test multiple hard fork scenario.

How

• Enhance sleep in devnet era markers script to remove some flakiness
• Fix transaction commands by leveraging the new era specific commands when available
• Enhance the test cases of the CI:
  • Test multiple versions of the Cardano node: 8.7.3 and legacy 8.1.2
  • Test hard fork transitions to Conway era at:
    • startup
    • few epochs after the startup
    • never