Added Iot credential usage to producer c samples #343

Job	Run time
address-sanitizer	45m 10s
arm32-cross-compilation	6m 4s
arm64-cross-compilation	6m 0s
clang-format-check	9m 34s
linux-aarch64-cross-compilation	6m 6s
linux-build-gcc-static	4m 5s
linux-gcc-code-coverage	44m 29s
mac-os-build-clang-local-openssl	52m 17s
mac-os-build-clang	1h 1m 24s
mac-os-build-gcc	1h 0m 22s
mac-os-build-gcc-local-openssl	59m 31s
mac-os-m1-build-clang	55m 12s
undefined-behavior-sanitizer	44m 17s
windows-msvc	55m 17s
ubuntu-gcc	46m 59s
	9h 16m 47s

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