fix(inputs.gnmi): Fix empty name for Sonic device

[srebhan]

• Updated associated README.md.
• Wrote appropriate unit tests.
• Pull request title or commits are in conventional commit format

resolves #12257

When used with a Sonic switch (4.0.2), the GNMI plugin produces an empty measurement name and in turn bails-out with Could not serialize metric: invalid name on the output side. The root cause of this is that the mentioned device reports the origin of the data as part of the first element in the form openconfig-platform:components for the update. This leads to a lookup error in the internal aliases map as usually the path is considered to be absolute and not including the origin.

This PR first adds two test-cases reflecting the debug data gathered from the (non-working) Sonic device as well as a working Arista device. It then adds an error in case the name cannot be determined to better track-down the root cause of future error cases. The PR then checks for the unusual reporting behavior and, if applicable, correctly splits the first element into the origin and path element thus fixing the issue.

[telegraf-tiger]

Download PR build artifacts for linux_amd64.tar.gz, darwin_amd64.tar.gz, and windows_amd64.zip.
Downloads for additional architectures and packages are available below.

👍 This pull request doesn't change the Telegraf binary size

📦 Click here to get additional PR build artifacts

Artifact URLs

DEB	RPM	TAR GZ	ZIP
amd64.deb	aarch64.rpm	darwin_amd64.tar.gz	windows_amd64.zip
arm64.deb	armel.rpm	darwin_arm64.tar.gz	windows_arm64.zip
armel.deb	armv6hl.rpm	freebsd_amd64.tar.gz	windows_i386.zip
armhf.deb	i386.rpm	freebsd_armv7.tar.gz
i386.deb	ppc64le.rpm	freebsd_i386.tar.gz
mips.deb	riscv64.rpm	linux_amd64.tar.gz
mipsel.deb	s390x.rpm	linux_arm64.tar.gz
ppc64el.deb	x86_64.rpm	linux_armel.tar.gz
riscv64.deb		linux_armhf.tar.gz
s390x.deb		linux_i386.tar.gz
		linux_mips.tar.gz
		linux_mipsel.tar.gz
		linux_ppc64le.tar.gz
		linux_riscv64.tar.gz
		linux_s390x.tar.gz
		static_linux_amd64.tar.gz