Consider default inclusion of `hardening-runtime` package

[JedMeister]

I think that it would be good to consider installing the hardening-runtime Debian package (new in Bullseye). The Debian readme provides more background and context.

I had been plannign to include it by default in v17.0, however following (mostly offline) discussion and contemplation of turnkeylinux/common#206, I am now thinking that this would be better with further consideration.

I may also write a blog post about it and suggest that users give it a go and report back.

[JedMeister]

I am thinking that this is more for documentation (and perhaps a blog post) rather than default inclusion (a least for now...).