Add Gecko Addon ID to make storage example compatible with Firefox
This PR adds an explicit addon ID to the with-storage example to make it compatible with Firefox.
This PR is connected to https://github.com/PlasmoHQ/storage/pull/12 - the exact reason for this change is added to the updated README there.
Adding this to the manifest will add a warning Unrecognized manifest key 'browser_specific_settings'. on Chrome as they don't seem to want to just ignore it. The warning has no further result though as the extension will work fine, and it also passes the Chrome WebStore review with this.
Let's use env for this instead!
Also, let's make sure the framework itself cleanup these browser specific stuff for chrome target.