[BUGFIX] Change location of default currency

[dahaupt]

This adjustment makes it easier to check the amount of available currencies.

Resolves: #303

[dahaupt]

@extcode Looking forward to your feedback or an alternative solution.

Edit: I will update the documentation after the changes are approved.

[extcode]

I'm not going to merge it like that. I see that this would be analogous to the available countries, but this is an avoidable breaking change. If this is to be included in the current version, it would have to be ensured that the old configuration takes precedence. There would have to be a change in the existing documentation. And another Rst would have to be created in the changelog to document these changes. I will write this on my note for the new version and TYPO3 v12.