Create an `about:health` page

To quote @ma1 and @thorin from tor-browser#41845 (closed)

(...) some kind of permanent sanity check (one global preference observer would do) which alerts users (in about:tor, about:preferences, about:config...) of every configuration change which we deem defeats Tor Browser's purpose (we've discussed this in Costa Rica, IIRC).

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an about:fingerprinthealth dashboard - including the extensions stuff (not bundled, web-accessible, etc) - something like TZP's attack template for css/engine/element/doc properties cover hundreds of pref changes - i.e we expect a deterministic result, and prototype/proxy changes can detect NoScripts signature for extensions

one issue here is this is a two edged sword, so we would need to word things carefully - i.e just because something is not detected (that affects your FP/health), doesn't mean it isn't there

We could maybe separate about:health and about:fringerprint in two different issues as well.