chore: document deprecation of timeout

[MyaLongmire]

Required for all PRs:

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

resolves #

Timeout was deprecated in 1.20.0 as we now call gosmi instead of snmptranslate but it was not documented.

[telegraf-tiger]

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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]

Just as a side note, you could have used the deprecation framework for this by

type SnmpTrap struct {
	ServiceAddress string          `toml:"service_address"`
-	Timeout        config.Duration `toml:"timeout"`
+	Timeout        config.Duration `toml:"timeout" deprecated:"1.20.0;no longer used"`
	Version        string          `toml:"version"`

[MyaLongmire]

That is in Thomas' pr here. We just want to note it in the readme in a release before we take his.