As not all Amazon marketplaces are natively supported, and because new
ones are regularly added by Amazon, this commit adds an exhaustive list
of supported marketplaces.
It also makes a few changes to the guide for adding an unsupported
marketplace in order to point the difference between an unsupported
and an incompatible marketplace.
task-2330255
- Removed the numbering from headings because it was either inconsistent, breaking the implicit hyperlink target or useless.
- Fixed incorrect heading formattings.
- Replaced hand-written flows by the :menuselection: directive