feat: improve sorting functionality in collectionGetHandler

The code changes in `handler.go` modify the `collectionGetHandler` function in the API handler. The changes introduce a more robust sorting functionality by splitting the sort parameter by comma and appending each part to the `clearedSort` slice. This allows for multiple sort criteria to be applied.

handler.go

@@ -136,8 +136,11 @@ func (api *API) collectionGetHandler(m mgocrud.ModelInterface) gin.HandlerFunc {
 		}
 		clearedSort := []string{}
 		for _, s := range sort {
-			if s != "" {
-				clearedSort = append(clearedSort, s)
+			// split by comma and append all parts to clearedSort
+			for _, sPart := range strings.Split(s, ",") {
+				if sPart != "" {
+					clearedSort = append(clearedSort, sPart)
+				}
 			}
 		}