Add --launcher-msg option to pass to desktop app

Summary:
Allows the launcher to provide messages to the user. Currently, in the form
of the red notification bar at the bottom. This is just meant as a temporary measure
during the alpha to have some clearly noticeable way of getting the user's attention.

I consider removing this a blocker for the release as this mechanism is not well
suited for this in many ways.

The current use case for this is providing a warning if a cached version is used
instead of the requested one, e.g. "Could not fetch requested Flipper version 'deadbeef', using cached version instead."

Reviewed By: jknoxville, priteshrnandgaonkar

Differential Revision: D14073687

fbshipit-source-id: 85630347027063103315eeb1286731fe2478e261

src/utils/processConfig.js

@@ -12,6 +12,7 @@ export type ProcessConfig = {|
   pluginPaths: Array<string>,
   lastWindowPosition: ?{x: number, y: number, width: number, height: number},
   screenCapturePath: ?string,
+  launcherMsg: ?string,
   updaterEnabled: boolean,
   // Controls whether to delegate to the launcher if present.
   launcherEnabled: boolean,
@@ -28,6 +29,7 @@ export default function config(): ProcessConfig {
       disabledPlugins: new Set(json.disabledPlugins || []),
       pluginPaths: json.pluginPaths || [],
       lastWindowPosition: json.lastWindowPosition,
+      launcherMsg: json.launcherMsg,
       updaterEnabled:
         typeof json.updaterEnabled === 'boolean' ? json.updaterEnabled : true,
       screenCapturePath: json.screenCapturePath,