docs(MADR): meshpassthrough design

[lukidzi]

Checklist prior to review

• Link to relevant issue as well as docs and UI issues --
• This will not break child repos: it doesn't hardcode values (.e.g "kumahq" as a image registry) and it will work on Windows, system specific functions like syscall.Mkfifo have equivalent implementation on the other OS --
• Tests (Unit test, E2E tests, manual test on universal and k8s) --
  • Don't forget ci/ labels to run additional/fewer tests
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? (this GH action will add "backport" label based on these file globs, if you want to prevent it from adding the "backport" label use no-backport-autolabel label) --

[lahabana]

I think this is worth adding a security consideration section.
Just to state that relying on labels means that it's important to consider that whatever users add there needs to be labels that service owners can't freely set as this would reduce the security posture.

However, someone could just have this reduced security posture and simply rely on auditing.

[lahabana]

LGTM just nits