fix: Update prometheus parser to be a new style parser plugin

[reimda]

resolves #11361

[reimda]

There are a couple prometheus settings that don't seem to do anything. I'm not sure if they are mistakes or if they were valid settings in the past and were removed, then intentionally left in so they will be ignored for backward compatibility.

• prometheus_ignore_timestamp
  • in missingTomlField
• prometheus_sort_metrics
  • in missingTomlField
  • in the prometheus serializer readme
  • in plugins/serializers/registry.go but unused elsewhere in code

I removed these in this PR but I'm having second thoughts. I need to figure out what to do with these before we merge this PR.

[srebhan]

Looks good to me. Just one comment regarding Init.
I think your option-removal is safe, but I would prefer to do the serializer one in an extra PR to be able to easily revert it if necessary.

[srebhan]

You can kill Init here and just return nil

Suggested change

	func (p *Parser) Init() error {
	return nil
	}
	func (p *Parser) InitFromConfig(config *parsers.Config) error {
	p.IgnoreTimestamp = config.PrometheusIgnoreTimestamp
	return p.Init()
	}
	func (p *Parser) InitFromConfig(config *parsers.Config) error {
	p.IgnoreTimestamp = config.PrometheusIgnoreTimestamp
	return nil
	}

[reimda]

I updated this to touch only the prometheus parser and to remove the empty Init()

[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_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 for migrating this one @reimda!