Added config validation

[NiklasVousten]

This allows to verify the config, as well as block and allowlists, without starting the DNS server

[NiklasVousten]

Added an additional --dry-run flag to syntax check the config, without starting the DNS server. This is different to --validate. Blocklists are not verified in this mode

[msrd0]

I'm not sure I like the use of cargo run over calling an installed command like crab-hole here. The readme so far only suggests installing this program, not running it in its source folder. @LuckyTurtleDev what do you think?

[NiklasVousten]

You are right. This should be changed.
Due to cargo being the only command listed, I just went with it.
I think it might be good to add an Running crab-hole section, or something similar.

Should this call the installed command, likely crab-hole, or just mention the additional flags?

[LuckyTurtleDev]

I personally would prefer to use sub commands for validate-lists and validate-config instead of flag. Since this are more like own commands and not like flags. So i would suggest to use clap derive for this. sub commands can be optional. so we can also keep the current behavior for crab-hole if it executed without arguments.

https://docs.rs/clap/4.5.22/clap/_derive/_tutorial/chapter_2/index.html#subcommands

Everything else looks fine 👍