Enhance documentation

[jpraynaud]

We need to enhance the documentation:

• Extract the documentation production in a separate workflow on the CI
• Make a separate website like on the Hydra.family and Hydra with Docusaurus

[Alenar]

Added nice website for the doc using Docusaurus in #106 , you can browse it here http://mithril.network/doc.
Next-steps:

• Reassess existing docs relevancy, ie: is docs/root/cardano-apis.md still needed ?
• Continue to adapt docusaurus base install to the projet: homepage text, theme colors ...