(Research) User Migration - User's added and enabled/disabled subscriptions

• User's added and enabled/disabled subscriptions remain in place after the extension updates from Mv2 to Mv3
• Handle error when user subscription is not available
• Handle error if limit of static rules is exceeded? (not sure if this happens at runtime or when extension is installed)

Integrator notes

• Webext SDK tries to detect the migration is needed and migrate the subscriptions to MV3 ones automatically. It happens after the webext updated. No calls from webext is needed.
• Once the MV2 MV3 migration happen webext should call EWE.subscriptions.getMigrationErrors(). It will return a list or (url, error) items where url is a subscriptions error and error is an error message. Once can also call EWE.subscriptions.clearMigrationError() to clear the errors and avoid showing it next time.
• It's suggested to test the bundled subscriptions to fit into Chromium limits (static rules limit, etc). In some cases like that Chromium might throw "Internal error" errors.