check should allow filtering at any config level

[johanneslumpe]

Right now we only support filtering at the group level using additional arguments to check. What we really want is the ability to filter at the group, application and/or dependency set level. Any of the following should be valid, given a matching config:

versionguard check

checks everything

versionguard check --group=a

check group a for all applications and dependency sets

versionguard check --group=a,b

check all applications in group a and b against all dependency sets

versionguard check --app=app

check app across all groups and sets. app should be resolved based on name or directory in the config. This should fail if app is not part of all groups.

versionguard check --group=a --app=app-a,app-b

check app-a and app-b against all dependency sets within group a

versionguard check --group=a --app=app-a --set=public

check app-a against dependency set public within group a

Any of the above should fail when specified combination is invalid. Once a use cases arises supporting a flag like --force or --ignore-mismatch can be discussed.