feat(inputs.snmp): Add displayhint conversion

[Hipska]

Summary

Add option to format the returned value from SNMP according to the textual convention from the MIB, for example the DateAndTime. The return type for this field will then be string.

Checklist

• No AI generated code was used in this PR
• Update processors.snmp_lookup docs
• Deprecate redundant conversion options

[srebhan]

Nice work @Hipska! Just one comment as we don't want implicit return-value declarations if avoidable.

[srebhan]

One more...

[srebhan]

Thanks @Hipska!

[telegraf-tiger]

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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