Support bulk adding fields to search_api index

I'm not working with SearchAPI at the moment, but that sounds useful.

Might be better in the SearchAPI module itself though, as it's fairly specific?

Thanks for the suggestion. Yes that could be a good place for it.

Just started with the issue fork here so that the community is aware if there is any interest.

I agree search_api or a separate contrib module might be a better place to start. If done here, it should be a separate submodule, I think.