🚀 Enhancement: Validate `serviceAccountJSON` File on the Fly

### 🔖 Enhancement description

At the moment, it is possible to upload a wrong, invalid or a blank JSON file for the FCM Provider. This is can later cause issues when sending a push notification.

See -

https://github.com/appwrite/appwrite/assets/20625965/bbbe01e1-e33a-4580-96fe-d0e33bb944e1

### 🎤 Pitch

Validate the `serviceAccountJSON` before uploading and creating the provider.

### 👀 Have you spent some time to check if this issue has been raised before?

- [X] I checked and didn't find similar issue

### 🏢 Have you read the Code of Conduct?

- [X] I have read the [Code of Conduct](https://github.com/appwrite/.github/blob/main/CODE_OF_CONDUCT.md)