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-server-core/src/plugins/PluginManager.tsx

@@ -138,7 +138,17 @@ export class PluginManager {
             }
           },
         });
-        if (response.headers['content-type'] !== 'application/octet-stream') {
+        function parseHeaderValue(header: string) {
+          const values = header.split(';');
+          // remove white space
+          return values.map((value) => value.trim());
+        }
+
+        if (
+          !parseHeaderValue(response.headers['content-type']).includes(
+            'application/octet-stream',
+          )
+        ) {
           throw new Error(
             `It looks like you are not on VPN/Lighthouse. Unexpected content type received: ${response.headers['content-type']}.`,
           );