add collections endpoint to nfts

nft/domain/opensea.go

@@ -1,9 +1,13 @@
 package domain
 
-type AssetResponse struct {
+type AssetsResponse struct {
 	Assets []*Asset `json:"assets"`
 }
 
+type CollectionsResponse struct {
+	Collections []*Collection `json:"collections"`
+}
+
 type Asset struct {
 	Id int32 `json:"id"`
 	TokenId string `json:"token_id"`