Docs: enhance era markers runbook

[jpraynaud]

Content

This pull request includes extensive updates to the docs/runbook/era-markers/README.md to improve clarity and ensure proper configuration for managing Mithril activation eras on the Cardano chain. The changes focus on enhancing the documentation format, updating environment variables, and providing detailed steps for setting up, bootstrapping, and updating era markers.

Documentation Improvements:

• Enhanced warning format for critical steps using [!IMPORTANT] and :fire: to emphasize potential risks. [1] [2]
• Added detailed instructions for setting up environment variables, including examples for both testnet and mainnet configurations.

Environment Configuration:

• Introduced new environment variables such as CARDANO_CLI, SCRIPT_TX_VALUE, and CARDANO_NETWORK_MAGIC to streamline the setup process.
• Updated commands to use the new CARDANO_CLI variable for consistency across the documentation. [1] [2]

Era Markers Management:

• Provided separate sections and detailed steps for preparing era markers, including handling single and multiple supported eras.
• Added verification steps to ensure the produced era markers are accurate and as expected.

Transaction Handling:

• Updated transaction commands to include --socket-path and use the new environment variables for better clarity and accuracy. [1] [2]
• Clarified the process for creating and submitting transactions, including retrieving transaction IDs and verifying UTxO states. [1] [2]

Pre-submit checklist

• Branch
  • Commit sequence broadly makes sense
  • Key commits have useful messages
• PR
  • No clippy warnings in the CI
  • Self-reviewed the diff
  • Useful pull request description
  • Reviewer requested

Issue(s)

Relates to #1946

[github-actions]

Test Results

    4 files  ±0     55 suites  ±0   10m 31s ⏱️ +5s
1 379 tests ±0  1 379 ✅ ±0  0 💤 ±0  0 ❌ ±0 
1 593 runs  ±0  1 593 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 01892ea. ± Comparison against base commit ef8c283.

♻️ This comment has been updated with latest results.