Use config json in home config directory to check metrics opt in status

[sukantoraymond]

Closes #615

Description

This PR uses config.json stored in user's local machine home config directory to check if user is opted in for metrics tracking

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[sukantoraymond]

Sample output of json in config.json

{
 "metrics": true
}

[sukantoraymond]

I also don't think we need go routine for sending command usage, because we are not aggregating the command usage. There is no limit on sending API events on mixpanel. Current implementation is fine.