fix: Read actual status code after a POST device API call

[FelixTing]

Also update the discovery example to v3.

fix: #452

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PR Checklist

Please check if your PR fulfills the following requirements:

• I am not introducing a breaking change (if you are, flag in conventional commit message with BREAKING CHANGE: describing the break)
• I am not introducing a new dependency (add notes below if you are)
• I have added unit tests for the new feature or bug fix (if not, why?)
• I have fully tested (add details below) this the new feature or bug fix (if not, why?)
• I have opened a PR for the related docs change (if not, why?)

Testing Instructions

Run EdgeX stack
Comment out the following code snippet:

device-sdk-c/src/c/devman.c

Lines 192 to 196 in e31ab6e

	if (existing)
	{
	edgex_device_release (svc, existing);
	continue;
	}

Build and run the discovery example (src/c/examples/discovery/template.c)
Add ProvisionWatcher

# at src/c/examples/discovery
curl -X POST [email protected] 0:59881/api/v3/provisionwatcher

Restart the example device service
Should be seeing logs related to device updates