Add documentation for node config file (.toml)

[joanestebanr]

related to #2056

Rationale

Currently, there is no documentation for the main config file of the node.
We need to include all information needed by somebody to create his own config file

Implementation

• We are going to generate a json-schema based on the config struct in code.
• The json-schema is going to be translate to html and markdown contents using the project json-schema-for-humans

This issue is based on the previous work of @arnaubennassar on the branch json-schema-doc