Mention hardware requirements and known issues before downloading and installing

Right now we have:

• https://tails.boum.org/doc/about/requirements/, for what hardware to have
• https://tails.boum.org/support/known_issues/, for what hardware not to have

But none of these are in the path of people installing Tails. So they will give it a try only to realize further down the line that Tails can't work on their machine.

• For PCs (except 32-bit), we've made huge progress with Secure Boot and Shift + Restart on Windows 10 and it would be super hard to tell people a lot more. But we should at least mention the basics: architecture and RAM.
• For Mac, it's still a nightmare and we could at least set better expectations (#17640 (closed)) and maybe provide lists of models that are known to work and known not to work.

All this should be integrated in the installation instructions.

For now, it could be done in the overview. See also #16808 (closed).

• PC
  • Mention RAM requirements
  • Mention architecture requirements and how to check
• Mac
  • Mention M1 in overview
  • Remove the hardware warning the success note on macOS (from #18074 (closed))
  • Embed the message drafted in #17640 (closed)
  • Replace the warning about keyboard and mouse with a note to let us know if it doesn't work (see #13576 (closed))
• Known issues
  • Link better between /install /doc/first_steps/start and /support/known_issues
  • Split known issues in "not at all" and "not entirely"
  • Use consistent heading levels