Config options missing from TOC

[SeanBryan51]

Not all config options are accessible in the table of contents for the documentation of config options. It looks like only headings will be rendered in the table of contents and options documented using custom links will not be included.

I was thinking we could organise the options to use a flat structure and use the data-toc-label to make hierarchical options clear in the table of contents. The flat structure also gives a consistent look for all the yaml options.