incus-user: unify logging, support --verbose and --debug

[bboozzoo]

Refactor logging setup so that it matches the rest of the code base. Add support for --verbose and --debug, similarly to other commands.

[stgraber]

Looks like the PreRun function needs a boilerplate comment.
I'd probably use something like:

// PreRun runs immediately prior to the main Run function.

[stgraber]

cmd/incus-user/main.go:57:	if err := run(); err != nil {

We don't do one-line define+check, so that should be split to:

err := run()
if err != nil {

[bboozzoo]

cmd/incus-user/main.go:57:	if err := run(); err != nil {

We don't do one-line define+check, so that should be split to:

err := run()
if err != nil {

Thanks for pushing a fix.