Do not check minimal fees on read only without fees

[AurelienFT]

• [x] document all added functions
• [x] try in sandbox /simulation/labnet
  • [x] if part of node-launch, checked using the resync_check flag
• [x] unit tests on the added/changed features
  • [x] make tests compile
  • [x] make tests pass
• [ ] add logs allowing easy debugging in case the changes caused problems
• [ ] if the API has changed, update the API specification