[Android] vpn/leo involuntarily cancellation

[deeppandya]

This issue primarily addresses the involuntary cancellation of VPN/Leo subscriptions.

It is a sub-issue of: [brave/brave-browser#37629](#37629).

Since Google Play does not provide specific details about the cancellation reason, we have two possible approaches to resolve this:

1. Real-time Subscription Monitoring – We can track subscription status in real time to detect cancellations and notify the client to display the appropriate UI.
2. API Call for Subscription Status – We can use the [Google Play Developer API](https://developers.google.com/android-publisher/api-ref/rest/v3/purchases.subscriptions/get) to fetch the subscription status by passing the purchase token and subscription ID, which the client can provide.

For option 2, the API response includes a cancelReason field with the following values:

• 0 – User canceled the subscription
• 1 – Subscription was canceled by the system (e.g., due to a billing issue)
• 2 – Subscription was replaced with a new one
• 3 – Subscription was canceled by the developer

Since we are specifically interested in involuntary cancellations (cancelReason = 1), we can use this response to trigger a UI notification on the client side, informing users about the cancellation.