Extract environment config initialisation to server-core

Summary: This diff makes most stuff that is read from the `os` package, and version info etc available from the `serverConfig` object, so that flipper-ui-core no longer needs the `os` package.

Reviewed By: passy

Differential Revision: D32694848

fbshipit-source-id: 93af1e95d898da9aaf351a6970b5a7652ee835c8

desktop/flipper-ui-core/src/dispatcher/plugins.tsx

@@ -210,7 +210,7 @@ export const checkDisabled = (
         config.env.FLIPPER_ENABLED_PLUGINS.split(','),
       );
     }
-    disabledList = config.processConfig.disabledPlugins;
+    disabledList = new Set(config.processConfig.disabledPlugins);
   } catch (e) {
     console.error('Failed to compute enabled/disabled plugins', e);
   }