Expand NCC's scope for other end-user migration tasks

[gamebits]

Is your feature request related to a problem? Please describe.
NCC currently serves the singular purpose of converting classic blocks to Gutenberg blocks. If we wished to widen that scope, it'd be amazing if NCC could perform other single-use functions, such as assigning featured images or excerpts. There may be some overlap with the Custom Content Migrator, but I'm thinking of those that aren't dependent on migrations from specific hosts or CMSes. See this repo for an example:

https://github.com/gamebits/easy-content-updates

It'd be amazing if we could build these functions into Newspack Content Converter, giving it a GUI interface similar to Yoast Test Helper, where users can push buttons for one-time functions (for example: instead of “Reset Indexables”, it’s “Assign Featured Images” or “Assign Excerpts”).

Describe alternatives you've considered
Right now, users and TAMs employ a hodgepodge of plugins, scripts, and utilities to get a site into tip-top shape post-launch. Let's combine them into a Swiss army knife!