chore: migrate to urfave/cli v3

[ldez]

The migration guide is sparse https://cli.urfave.org/migrate-v2-to-v3/, but the migration is not complex.

[dmke]

LGTM

[ldez]

I have the feeling after playing a bit with urfave/cli v3 that not all things are stable, so we will wait a bit before the merge of this PR.

[ldez]

v3.2 of urfave/cli breaks things... I always appreciated the simplicity of this lib, but the current release flow is bad, very bad.

[dmke]

I mean... if upgrading urfave/cli to v3 is this tedious, we can stay on v2 for a while longer.

Have you looked into alternatives, yet? Personally, I found spf13/pflag sufficient most of the time, and spf13/cobra helpful for anything beyond.

[ldez]

I use spf13/cobra (+ spf13/viper) for other projects, IMHO it's overkill for lego.
It needs plumbing and has unwanted complexity, especially when using spf13/viper.
spf13/viper has some design problems (it creates "case insensitivity" by lower-casing everything, and this is a problem).

IMHO, spf13/pflag is not a huge improvement on the standard flags package, and it has the same problems as spf13/cobra (expected as spf13/cobra is based on spf13/pflag).

I'm looking at alecthomas/kong, I never tried.

I also created a configuration parser a few years ago: traefik/paerser

But I still like the simplicity of urfave/cli.

For now, we don't need to migrate, so we will wait.