F OpenNebula/one#6682: Refactoring OneFlow docs

[vickmp]

Description

All OneFlow documentation has been refactored:

1. The main OneFlow documentation has been completely restructured:
   • All sections have been reorganized to give a logical flow to the content.
   • New sections have been added to cover OneFlow’s features.
   • More examples and basic explanations have been added to help new users understand OneFlow.
   • Some additional Sunstone images have been included.
   • Some sections have been updated to adapt to the new features.
2. The API documentation page has been updated, with attribute names revised and information on the new features added.

Branches to which this PR applies

• master