On ice until after GA
```[tasklist]
# Before merging
- [x] Re-frame it as upgrading the Linux CLI to add IPC / systemd autostart support instead of replacing the CLI (thanks Thomas)
```
Internal (Not private, just un-interesting to most users) docs and
research to explain the DNS control methods.
I think Jamil was right, we should revert `/etc/resolv.conf` on exit in
case it's used on some minimal Debian kitten. We can keep that and the
`systemd-resolved` method around to support desktop Ubuntu. Everything
else is going to be "When someone needs it".
Right now it only works on my dev VM, not on my test VMs, due to #4053
and #4103, but it passes tests and should be safe to merge.
There's one doc fix and one script fix which are unrelated and could be
their own PRs, but they'd be tiny, so I left them in here.
Ref #4106 and #3713 for the plan to fix all this by splitting the tunnel
process off so that the GUI runs as a normal user.
Closes#3862
I refactored the settings code, removing `_settings_` from some function
names where it was redundant.
The log level is more difficult to change live, so I added a
`tracing::info!` noting that it will apply on next app start.
```[tasklist]
### Before merging
- [x] Document whether pressing Enter on a field to apply settings is intended behavior
- [x] Document that log levels don't apply until next app start
- [x] Document that auth and API URL apply on next sign-in
```
This may cause conflicts with all my other PRs but it has to happen.
```[tasklist]
- [ ] Update test names in branch protection (I don't think I have perms for this)
```
