Fix WARNING: duplicate label

[ItsDrike]

When including a document that contains multiple headings with exactly the same names, such as a changelog like this:

# Version 1
## Bugfixes
- A
- B
- C

# Version 2
## Bugfixes
- A
- B
- C
## Features
- X
- Y

The h2 headings are duplicated, and so duplicate label warnings appear.

A potential solution to this could be to replicate what MyST is doing, and use placeholder ids like #id1, #id2, etc. for any such duplicate labels, to allow referencing any title easily, without any conflicts.

i.e. the final version shouldn't look like this:

But rather like this:

[ReenigneArcher]

+1, I'm also wanting to include changelog in my docs. Only solution I have found is to use

**Heading** instead of ## Heading, but it's not ideal.