Enable Marketplace for Flipper (#3491)

Summary:
This is PR on top of: https://github.com/facebook/flipper/pull/3473

It adds an option to Settings to allow distribution of marketplace plugins.

Also includes a simple fetch function to retrieve data from external API/server.

## Changelog

Allow marketplace plugins

Pull Request resolved: https://github.com/facebook/flipper/pull/3491

Test Plan:
1. Enable marketplace
2. Provide custom marketplace server (it will serve the list of internal plugins with downloadURL)
3. Test if can see Available plugins and can download/remove the plugin
4. If new update for the plugin, it should also allow auto update

Reviewed By: antonk52

Differential Revision: D34586339

Pulled By: nikoant

fbshipit-source-id: c887982aa0f0f9abd3b5360f22e8692a2445d345

desktop/flipper-ui-core/src/fb-stubs/pluginMarketplaceAPI.tsx

@@ -8,9 +8,22 @@
  */
 
 import {MarketplacePluginDetails} from '../reducers/plugins';
+import {Store} from '../reducers/index';
 
-export async function loadAvailablePlugins(): Promise<
-  MarketplacePluginDetails[]
-> {
-  return [];
+export async function loadAvailablePlugins(
+  store: Store,
+): Promise<MarketplacePluginDetails[]> {
+  const {enablePluginMarketplace, marketplaceURL} =
+    store.getState().settingsState;
+  try {
+    if (!enablePluginMarketplace && !marketplaceURL) {
+      throw new Error('Marketplace is not enabled');
+    }
+    const response = await fetch(marketplaceURL);
+    const plugins = await response.json();
+    return plugins;
+  } catch (e) {
+    console.error('Failed while retrieving marketplace plugins', e);
+    return [];
+  }
 }