feat: Add prefix and suffix to the advanced_join fragment

[sudojunior]

Currently the fragment covers each element it receives as nodes. Each node is a predefined structure and only those properties are used in the fragment.

# advanced_join fragment schema
- !!node
  target: !!str | !!str[]
  char: !!str = ", "
  last: !!str = " and "
  connector: !!str = "; "

This also intended was to improve readability of the fragment to track how it constructs a string and to make room for formalized sub fragment injection. How this will happen is currently unknown, but the addition of prefix and suffix may require some reorganizing in the control flow and overall structure of what should be prioritized.

Original idea

Remove connector, then replace with prefix and suffix.

I now see that another approach should be used here, to ensure its deployment is clear to other contributors.