Switch to Pythagoras era

[jpraynaud]

Issue

Create a new Pythagoras era that updates the enables signature of the Mithril Stake Distribution entity type (and Open API version from 0.1.x to 0.2.0)

To do

• [x] Prepare the new Pythagoras era
  • [x] Enable Mithril Stake Distribution open messages on the new Pythagoras era
  • [x] Bump Open API version to a new minor 0.x version (which is a breaking change) on the new Pythagoras era
  • [x] Deactivate the redirect routes of the snapshots for the new Pythagoras era
  • [ ] Add a message v2 for snapshot artifacts (with new locations format)
• [ ] Distribute the new Pythagoras era
  • [ ] Create a new distribution that embeds the new Pythagoras era
  • [ ] Create dev blog post
  • [ ] Announce the new Pythagoras era to incompatible nodes
  • [ ] Monitor the deployment of the new era compatible version on the signer nodes
    • [ ] testing-preview network
    • [ ] pre-release-preview network
    • [ ] release-preprod network
  • [ ] Activate the new era when enough signer can run the new era
    • [ ] testing-preview network
    • [ ] pre-release-preview network
    • [ ] release-preprod network
  • [ ] Clean the previous Thales era

Reasons to create a new era

• Sign beacons
• Switch optional values to standard values in message