Handle pagination for the federated actions & followers responses (#1731)

* Add pagination for admin social list

* Use Paginated API for followers tab on frontend

router/middleware/pagination.go

@@ -0,0 +1,39 @@
+package middleware
+
+import (
+	"net/http"
+	"strconv"
+)
+
+// PaginatedHandlerFunc is a handler for endpoints that require pagination.
+type PaginatedHandlerFunc func(int, int, http.ResponseWriter, *http.Request)
+
+// HandlePagination is a middleware handler that pulls pagination values
+// and passes them along.
+func HandlePagination(handler PaginatedHandlerFunc) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		// Default 50 items per page
+		limitString := r.URL.Query().Get("limit")
+		if limitString == "" {
+			limitString = "50"
+		}
+		limit, err := strconv.Atoi(limitString)
+		if err != nil {
+			w.WriteHeader(http.StatusBadRequest)
+			return
+		}
+
+		// Default first page 0
+		offsetString := r.URL.Query().Get("offset")
+		if offsetString == "" {
+			offsetString = "0"
+		}
+		offset, err := strconv.Atoi(offsetString)
+		if err != nil {
+			w.WriteHeader(http.StatusBadRequest)
+			return
+		}
+
+		handler(offset, limit, w, r)
+	}
+}