Add VaccineNameDetails into an existing hierarchy

[lache-melvin]

It feels like it would be nice to have a way to add the level into an existing hierarchy.
Like if we start with Just Influenza then later decide to split it to Seasonal variations.
I don't think that's super straightforward unfortunately but maybe worth creating a new issue for it?

Originally posted by @jmbrunskill in #538 (review)

VaccineNameDetails is an optional field between Form and ActiveIngredients. However, it can only be added between them when creating new branches off of the Form (i.e. before adding ActiveIngredients).

It would be great to allow inserting the VaccineNameDetails after ActiveIngredients and their children have been defined.