How to generate feeds with different data structures?

Hi @introfini, thanks for your work! I'd expect the code as-is to experience caching issues connected with #3240612: Allow extra cache keys per feed → . Eg. in a contrived example if you preprend G to the variation title in a google feed, and F to a Facebook feed title, and run the following two commands one after the other, I'd expect all product titles in both feeds to have G at the start due to cached normalizations.

drush product-feed:generate google.xml --tag=google
drush product-feed:generate facebook.xml --tag=facebook

Separately, note it's already possible to "alter in" custom options to existing drush commands, which is how I've added a similar option to feed generation in the past (we needed an --assume-in-stock option for feeds that weren't automatically updated). But it's a bit of a bother altering a drush command, so I can see the case for a tag option.

Setting to NW due to expected caching issues. Thanks again!