feat: Add caching to internet_speed

[Jleagle]

Required for all PRs:

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

This PR adds two config options, offset & cache.

Offset is to help spread the calls to the speedtest server, this also reduces errors that seem to happen at specific times like on the hour, presumably where everyone does a test at the same time.

Cache caches the closest speedtest server, there doesn't seem to be much point in querying all the servers to get the closest one when it's going to be the same every time.

They both default to false to help with backwards compatibility.

[telegraf-tiger]

Thanks so much for the pull request!
🤝 ✒️ Just a reminder that the CLA has not yet been signed, and we'll need it before merging. Please sign the CLA when you get a chance, then post a comment here saying !signed-cla

[Jleagle]

!signed-cla

[srebhan]

Thanks for this PR @Jleagle. I have some comments in the code. However, there is a more general comment regarding the offset. I think this should be a Telegraf-wide option to allow an offset to the rounded gather interval globally and plugin-wise. So I'm setting the corresponding tag to make Influx people take a look.

[srebhan]

The corresponding issue is #10406 and #1319.

[srebhan]

@Jleagle can you maybe check if you can get rid of the offset parameter in your PR when rebasing on #10545 and using collection_offset!?

[srebhan]

Very nice @Jleagle. There is only one offset left-over in the readme, but other than that we are fine to go I think.
Just one more request: If the collection_offset worked for you, please drop a note in the corresponding PR. Thanks for your effort!

[telegraf-tiger]

☺️ This pull request doesn't significantly change the Telegraf binary size (less than 1%)

📦 Looks like new artifacts were built from this PR.

Expand this list to get them here ! 🐯

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_i386.zip
armel.deb	armv6hl.rpm	freebsd_amd64.tar.gz
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

[srebhan]

Looks good to me. Thanks @Jleagle for your contribution!

[Hipska]

I'm a bit late to the party, but now the selected server is used for the whole duration of telegraf run. I can imagine after a few days that server is not available and another one should be picked.

Could someone implement server re-election and/or cache expiry (Duration)?

[srebhan]

I think re-electing the server on error is a valid point.