sd-log tries to log to itself, but loopback qrexec connections aren't supported

[eaon]

While looking into policy changes/details this stuck out to me: qrexec: securedrop.Log: sd-log -> sd-log: denied: loopback qrexec connection not supported. @conorsch confirmed this also affects 4.0 when we briefly touched on this in passing in #751, but I think this is worth breaking out for a different reason:

On 4.0 this denial is silent for users, but 4.1 ramped up user facing reporting of such denials, so this triggers a fairly alarming ⛔ notification visible when running the preflight updater:

While it's functionally not a problem as far as I've gathered, this may warrant handling to improve the optics.

[eaon]

While looking into qrexec for another project over the weekend, freedomofpress/securedrop-client#1721 graced my screen. I believe by simply installing the proposed log-server but not log-forwarder package onto sd-log this denial wouldn't come up anymore.