docs: maintainers_include: improve its output

docs: maintainers_include: improve its output

There are three "types" of profiles:
1. Profiles already included inside subsystem-specific documentation.
   This is the most common case;
2. Profiles that are hosted externally;
3. Profiles that are at the same location as maintainer-handbooks.rst.

For (3), we need to create a TOC, as they don't exist elsewhere.

Change the logic to create TOC just for (3), prepending the
content of maintainer-handbooks with a sorted entry of all types,
before the TOC.

With such change, we can have an unique sorted list of profiles,
having the subsystem names used there listed.

Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <10d06a3f530e07ad981aba93617a9a7f4d63c408.1777295258.git.mchehab+huawei@kernel.org>