Activate Pythagoras Mithril era

[jpraynaud]

Why

The support code for the Pythagoras Mithril era has been added in #1946. The era switch needs to be executed once the threshold of 95% of compatible signer nodes is reached (running a version >= 0.2.182).

What

Activate the Pythagoras era on the public Mithril networks and then remove the previous Thales epoch.

How

• Prepare a rollout plan for the new Pythagoras era in the public Mithril networks:
  • pre-release-preview
  • release-preprod
  • release-mainnet
• Once the Pythagoras is activated in th epublic Mithril networks:
  • Activate the new era on the testing-sanchonet network
  • Cleanup the Thales era in the code