goldmark: Add options footnote.BacklinkHTML, table.ClassCellLeft, table.ClassCellCenter, table.ClassCellRight

[10maurycy10]

Currently, the hugo configuration file can only enable or disable the Footnote extention to goldmark. The reson for this is that the allowed properties are hardcoded in hugo. The only option for Footnotes and all other extentions other then Typographer is to enable or disable it.

Idealy, this would be implemented in a way that just passes configuration to goldmark, allowing full access to goldmark configuration. If that is infeasible, simply adding more configurability to the markdown engine would be good.

[jmooring]

Of the extension options that are not configurable, only one has any meaningful value by simply exposing it: WithFootnoteBacklinkHTML. This would allow you to change the back arrow below into whatever:

This has come up 2 or 3 times in the forum, but mostly related to the transition from Blackfriday to Goldmark several years ago (the option was exposed with Blackfriday). It's a nice-to-have, but there's little/no demand.

The table extension has a WithTableCellAlignMethod option, but simply exposing this doesn't buy us anything. We'd need to create our own options, related to TableCellAlignNone, allowing us to specify classes for left, right, and center aligned td and th elements. Currently we get this:

Inline styling can be blocked by CSPs, so doing something in this area is probably a good idea, at some point. But similar to WithFootnoteBacklinkHTML, this is currently just a nice-to-have.

Related: #7244

[bep]

I have made the issue title more ... to the point.

Note that doing this would require revising these options to be struct types on the same form as the cjk extension.