TelemetryClient constructor taking instrumentation key?

[zooba]

It would be nice to be able to construct a TelemetryClient with just a key, rather than having to remember about setting it via context.

tc = TelemetryClient('12345678-1234-1234-1234567890')

Since the first parameter can currently only be a TelemetryChannel, it seems easy enough to test for that type.

Maybe there's some reason why it makes sense to disallow this, but I can't think of it myself.

[BogdanBe]

The instrumentation key is always required so there is no good reason why we would want to create a client that doesn't have have one. As such we will add an additional (required) parameter to the ctor of TelemetryClient

To maintain (some) backwards compatibility cases, we will test the first parameter for the TelemetryChannel type and we will not raise an exception in this case.

[BogdanBe]

Fixed in #9