Increase timeout for successful signing about sign-addon

[diox]

In addition, I don't know if it's off-topic here and only for web-ext, but even if we patch the timeout, it might makes sense for web-ext to return without an error when the timeout has been reached, if the upload is marked as valid.

It would mean that although it passed linting and basic validation rules, signing has not been done yet, for whatever reason, but is expected to happen eventually.

We already have code that does this for listed uploads, relying on the automated_signing property returned by AMO API, but that property has been a bit misleading for a while: A lot of uploads are now auto-approved, even listed, but we still (currently and in the future) return "automated_signing": false for those.

[diox]

Building on my previous comment, here is how I think it should work from a user perspective:

• Validating add-on pseudo progress bar is marked as finished as soon as polling detects valid is true on the upload, otherwise reports an error and terminates the process
• If validation was successful a second pseudo progress bar is started, Signing add-on
• Once signed is true, everything behaves as before
• If timeout is reached, return with the following message: Your add-on has been submitted for review. It passed but could not be automatically signed, you'll receive an email when it is available for download and terminate.