Add error handling when Amplify AppId is invalid and doesn't exist in the configured region

[Amplifiyer]

Environment information

N/A

Describe the bug

When appId is provided as an input argument for any of the cli commands, there is currently no validation that it exists in the Amplify service in the configured account and region. We should detect it and notify customers about it before it fails in the service.

Reproduction steps

e.g. running this command npx ampx generate graphql-client-code --app-id d1st9sfxoeuu3r --branch mybranch with invalid app-id throws service error

[amazon-q-developer]

✅ I finished the proposed code changes, and the pull request is ready for review: #10.

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