Allow ConflictsWith, ExactlyOneOf, and AtLeastOneOf to work in Lists

[megan07]

Use-cases

Currently ConflictsWith, ExactlyOneOf or AtLeastOneOf are set at the attribute level, which means we can't set it on a list of if we have a list of objects, and each object has a list of attributes that's AtLeastOneOf. We don't know the length of the list and there is no way to differentiate object[0] from object[1] with what is conflicting.

Proposal

We need to move ConflictsWith, ExactlyOneOf and AtLeastOneOf to the resource level to be able to determine which child fields are conflicting.

[bflad]

Just to document them, other (potentially mutually exclusive) ideas that have floated around this space are:

• Support for "relative" attribute paths (e.g. starting with a period to reference the same index of list/set block)
• Support for "wildcard" attribute paths (e.g. having an asterisk would match any index within a list/set block)