feat: Add function to ensure trailing numbers are removed from heading anchors

Done

Adds a function _remove_trailing_numbers_from_headings to the base soup parser that ensure trailing numbers are removed from heading anchors

Specify this branch as the requirement for canonicalwebteam.discourse, it will look something like:

canonicalwebteam.discourse @ git+https://github.com/canonical/canonicalwebteam.discourse@remove-trailing-numbers

Run dotrun clean to remove any old packages and then dotrun to reinstall
If that doesn't work you can download the canonicalwebteam.discourse and check out this branch and then add
```
-e ../canonicalwebteam.discourse
```
where the requirement for canonicalwebteam.discourse would be (I'm assuming they live in the same folder here)
Once it is running with this branch, do to any docs page and check that the headings contain an anchor that doesn't have a trailing number. eg.
```
<h2><a class="anchor" href="#in-this-documentation" name="in-this-documentation"></a>In this documentation</h2>
```