Allow footnotes filter to be after the 'Limit allowed HTML' filter

Problem/Motivation

If the footnotes filter is after the limit allowed HTML filter, the footnotes do not get outputted. The reason is that they are not in the allowed tags, so currently the filter must be processed before the limit allowed HTML.

Steps to reproduce

Place the footnotes filter after limit allowed HTML
No footnotes are output

Proposed resolution

Add these to options to the ckeditor yml file in the root of the module:

<footnotes>
<footnotes data-text data-value>

Update the module homepage to remove this step.

Remaining tasks

Create MR

User interface changes

None

API changes

None

Data model changes

None