[Transformers] Deprecate neosync transformers

[eminano]

Given the recent archival of the neosync project, we will want to stop supporting the library eventually. In order to do that, we should have equivalent transformers to the neosync ones pgstream currently supports, so that anyone using them can smoothly transition.

The currently supported neosync transformers are:

• Email transformer (we have a custom alternative )
• First name transformer (we have greenmask transformer as alternative)
• Last name transformer
• Full name transformer
• String transformer (we have a custom and a greenmask alternative)

In order to fully deprecate neosync transformers, we only need to add support for last name and full name transformations, since the rest have already alternatives, either from custom or greenmask transformers.