Additive tagging for multi item editing

[alexjmck]

Is your feature request related to a problem? Please describe

When tagging multiple items (books and series) there is only an option to overwrite tags, genres, authors etc. It can be frustrating when adding new tags to existing works when editing my library.

Describe the solution you'd like

It would be incredibly helpful to allow preserving the existing tags and having the option to add additional ones to them. Currently you have to override tags when you use the bulk editor.

Describe alternatives you've considered or other apps that can do what you want

I'm unsure of how alternative apps do this. The only work around to my knowledge is to edit each item individually.

Additional context

These are the screens in question:

The screen when editing multiple series.

The screen when editing multiple books.

Thank you to everyone who has put work into this platform. I appreciate it a lot when I use this platform for my daily reading.