docs: clarify when you use getServerSideProps (#35922)
Removed the misleading TTFB information. It was easy to read that incorrectly and while getStaticProps does have a better TTFB that's not why you might need to avoid getServerSideProps, I gave better examples.
I also wanted to answer "well how do I cache `getServerSideProps`?" and now there's a link.
## Documentation / Examples
- [x] Make sure the linting passes by running `yarn lint`
