Add attribute flag building and parsing (#1562)

This adds a few command sketches but that's not the main point of the PR
and filling those out will come in a different PR. This adds a new flag
type that can combine inputs to a single target slice, retaining the
ability to distinguish where it came from but also keep ordering across
different flag names. It also implements a function that does the
heuristic parsing with fallback.

api/hostsets/option.gen.go

@@ -74,6 +74,18 @@ func WithFilter(filter string) Option {
 	}
 }
 
+func WithAttributes(inAttributes map[string]interface{}) Option {
+	return func(o *options) {
+		o.postMap["attributes"] = inAttributes
+	}
+}
+
+func DefaultAttributes() Option {
+	return func(o *options) {
+		o.postMap["attributes"] = nil
+	}
+}
+
 func WithDescription(inDescription string) Option {
 	return func(o *options) {
 		o.postMap["description"] = inDescription