feat(tools): Allow to markdown includes for sections

[srebhan]

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

related to #11691
fixes: #9065

This PR extends the readme_config_includer in two ways. First, it allows global includes relative to the Telegraf project root by specifying an absolute path (e.g. /docs/bla.md).
Additionally, the tool now also allows to replace sections of the document by providing include(s) at the header level. For example in the following README:

Some text
[...]
## My included part <!-- @/docs/include/replacement.md -->

more text, code, also
multi-line text

or 
additional paragraphs, etc as well as

### Subsections

as long as they have a deeper 
level (more hashes) are replaces until

## A heading on the same level

occures.

everything after ## My included part <!-- @/docs/include/replacement.md --> and before ## A heading on the same level is replaced by the content of /docs/include/replacement.md. The result is stable as long as the included file will not insert headings on a lower or equal level compared to the include heading.

[powersj]

I think this is exactly what we wanted! The restriction of:

The result is stable as long as the included file will not insert
headings on a lower or equal level compared to the include heading.

Is totally fine way of limiting what this replaces and puts in as well.

Thank you!

[powersj]

I'm ready to merge this, but there are two lint errors we will want to clean up:

/github/workspace/docs/includes/plugin_config.md:1 MD041/first-line-heading/first-line-h1 First line in a file should be a top-level heading [Context: "In addition to the plugin-spec..."]
/github/workspace/docs/includes/plugin_config.md:6:50 MD047/single-trailing-newline Files should end with a single newline character

The first should be ignored especially if we add future of these types of markdown docs

The second you should fix. Will this add an extra new line between sections?

[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