Bug: Lack of validation in cleaning manifest data

[IKarbowiak]

What are you trying to achieve?

The KeyError is raised when manifest_data doesn't have tokenTargetUrl.

Steps to reproduce the problem

1. Run AppFetchManifest with URL that contains JSON data without tokenTargetUrl.
2. You will get the KeyError.

What did you expect to happen?

The ValidationError should be raised.

Logs

https://sentry.io/organizations/saleor/issues/3749157627/?project=6417854

Environment

Saleor version: 3.9 (to check if it also affect other versions)