feat(serializers): Add CloudEvents serializer

[srebhan]

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

resolves #10170

This PR adds a serializer to convert Telegraf metrics into the CloudEvents JSON format.

[powersj]

Thanks for this!

Can I suggest tossing your batch-metrics expected.json output into a JSON Schema validator along with the cloudevents schema. I noticed that the timedev claims it must match RFC 3339 (e.g. 2018-04-05T17:31:00Z)

Otherwise I think this is nearly good to go. Let me know what you think about the time one and I can give this a more complete review

[powersj]

+1 thank you for researching the timestamp.

Needs an update to resolve a conflict in go.mod. Feel free to merge once fixed.

[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 increases the Telegraf binary size by 5.46 % for linux amd64 (new size: 184.7 MB, nightly size 175.1 MB)

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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_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