Evaluate snapshot solution in regards to pricing

Created by: eseliger

With the addition of more snapshot tests, we are facing much higher pricing for percy. We should evaluate if we get the value out of it and whether there are other solutions that fulfill our needs better (or are cheaper). See this comment https://github.com/sourcegraph/sourcegraph/pull/10622#issuecomment-628568750 on context. One suggestion from @felixfbecker was to use https://www.chromatic.com/ for storybook snapshots, which are more tailored to storybook as well (but aren't particularly cheaper).

as a first reduction, I disabled Firefox snapshot tests, which cut down usage by 50%.

@felixfbecker assigning you here, can you own evaluating that?