Improve Error Message for Invalid Credentials

[AlexCatarino]

Similar to #16

Expected Behavior

401 Unauthorized explain that credentials are invalid.

Actual Behavior

We receive the following message which doesn't explain 401:

During the algorithm initialization, the following exception has occurred: Error getting cash balance from brokerage: CoinbaseApiClient.ExecuteRequest failed: [401] Unauthorized, Content: Unauthorized

Potential Solution

If the error code is 401. Ask user to verify credentials.
API Private Key is tricky since members need to remove \n which might lead to human error.

Reproducing the Problem

Deploy with old/invalid credentials.

Checklist

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• I have confirmed that this is not a duplicate issue by searching issues
• I have provided detailed steps to reproduce the issue