Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

internal/api/icon.go

@@ -0,0 +1,37 @@
+// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package api // import "miniflux.app/v2/internal/api"
+
+import (
+	"net/http"
+
+	"miniflux.app/v2/internal/http/request"
+	"miniflux.app/v2/internal/http/response/json"
+)
+
+func (h *handler) feedIcon(w http.ResponseWriter, r *http.Request) {
+	feedID := request.RouteInt64Param(r, "feedID")
+
+	if !h.store.HasIcon(feedID) {
+		json.NotFound(w, r)
+		return
+	}
+
+	icon, err := h.store.IconByFeedID(request.UserID(r), feedID)
+	if err != nil {
+		json.ServerError(w, r, err)
+		return
+	}
+
+	if icon == nil {
+		json.NotFound(w, r)
+		return
+	}
+
+	json.OK(w, r, &feedIconResponse{
+		ID:       icon.ID,
+		MimeType: icon.MimeType,
+		Data:     icon.DataURL(),
+	})
+}