Review Mozilla 1848815: Add a user-facing setting to enable enterprise roots import, and enable it by default

The checkbox seems to be disabled by default for us, but maybe we'll prefer to hide this setting again.

Interestingly, I don't see it on Linux, but I see it on my Windows VM (it's below OCSP, as per the screenshot from the Bug).

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information