Changes required for distributed tracing instrumentation

[t-manyadav]

There are few changes required/remaining for distributed tracing instrumentation: #201

• Activity name should not be "Trigger" instead we can use Function app name.
• Need to add custom properties tag for created activity, so that we can have more metadata about activity.

[JatinSanghvi]

@t-manyadav - Can you explain or share a link that explains what custom properties are?