Fix naming of nested object arrays in Storyblok converter

[julrich]

Currently names are derived using some (lacking) inference from JSON Schema keywords (like title, key of the field, etc), resulting in inconsistencies, and especially some cases where a singular should be used in naming of repeated objects, instead of the (currently chosen) plural version.

There was some work done for this in our Netlify Create converter, that could be of guidance, here:
e67e073