Improve cli about woodpecker

[xoxys]

@woodpecker-ci/maintainers I would like to work on improve error handling for missing args (missing repo id / name results in an parseInt error atm) How do we want to handle it? Do we really want to continue using args? IMO, it would be better to drop args completely and just use flags. Any reason to keep using args?

[anbraten]

I think its quite common practice to use args (see kubectl, docker, ...) therefore I would suggest to stick to it and add an empty-string check with a more descriptive error in front of the parseInt call.

[xoxys]

Obviously, but I could also name a lot of tools without args. We could have a way more clean code without arg validation, as flag validation and required flags is a built-in feature of urfave/cli. However, if args is preferred, that works for me as well.

[lafriks]

I don't know if urfave/cli still checks that required arguments are not empty if required (you can provide argument but provide it with empty value) so check for empty value could still be needed

[xoxys]

There is no required args feature, just a required flags option.