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

Also update the discovery example to v3.

fix: #452

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PR Checklist

Please check if your PR fulfills the following requirements:

[x] I am not introducing a breaking change (if you are, flag in conventional commit message with BREAKING CHANGE: describing the break)
[x] 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?)
[x] 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?)

Run EdgeX stack Comment out the following code snippet: https://github.com/edgexfoundry/device-sdk-c/blob/e31ab6e2f568dd8fbe7ffcfa2103cfb092f62c0d/src/c/devman.c#L192-L196 Build and run the discovery example (src/c/examples/discovery/template.c) Add ProvisionWatcher

# at src/c/examples/discovery
curl -X POST -d@watcher1.json 0:59881/api/v3/provisionwatcher

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