feat(inputs.radius): Provide setting to set request IP address

[powersj]

Summary

Checklist

• No AI generated code was used in this PR

Related issues

fixes: #14962

[srebhan]

@powersj according to RFC2865 the field (or NAS-Identifier) MUST be present for the access-request packet we are sending. So I think we should add a nas_identifier option and use this or determine the LocalAddr of the client and use it as NAS-IP-Address...

[powersj]

While the RFC says that, our integration tests demonstrate that it is not required. Changing that to always be present would make this potentially a breaking change, hence why this is opt-in.

[powersj]

PR updated with the default set to 127.0.0.1 if empty.

[srebhan]

Looks good. My only comment would be to reference the term NAS-IP-Address or we name the option like this (as you had before :-()... Not sure which approach is better....

[telegraf-tiger]

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🥳 This pull request decreases the Telegraf binary size by -2.88 % for linux amd64 (new size: 224.8 MB, nightly size 231.4 MB)

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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