Remove unnecessary cache clearing

I was looking at what gets flushed in the submits, and we definitely invalidate:

config:legal.settings
legal_conditions_list

However, with the killswitch on the Page cache, I'm unsure as to whether this is enough. I wonder whether some more in-depth caching should be integrated? But I do not believe we need to flush all of the caches. I've added extra contexts/tags to the controller for good measure.

Patch based on the MR