translate maps to sequences in pkg metadata (#2553)

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

syft/pkg/key_value.go

@@ -0,0 +1,28 @@
+package pkg
+
+type KeyValue struct {
+	Key   string `json:"key"`
+	Value string `json:"value"`
+}
+
+type KeyValues []KeyValue
+
+func (k KeyValues) Get(key string) (string, bool) {
+	for _, kv := range k {
+		if kv.Key == key {
+			return kv.Value, true
+		}
+	}
+
+	return "", false
+}
+
+func (k KeyValues) MustGet(key string) string {
+	for _, kv := range k {
+		if kv.Key == key {
+			return kv.Value
+		}
+	}
+
+	return ""
+}