feat: add remarkPlugins theme option

[alaaalii]

Add a remarkPlugins option to pass along to gatsby-plugin-mdx.

The reason this is required in addition to the gatsbyRemarkPlugins option is because gatsbyRemarkPlugins has had numerous issues with getting plugins to work with it:

• [gatsby-remark-katex] Doesn’t work with gatsby-plugin-mdx gatsbyjs/gatsby#21866
• [gatsby-plugin-mdx] gatsby-remark-mathjax doesn't work gatsbyjs/gatsby#16983
• Can't bind plugin via setParserPlugins option with gatsby-transform-remark gatsbyjs/gatsby#8009
• How to use remark-bracketed-spans with gatsby-transformer-plugin? gatsbyjs/gatsby#9103
• gatsby-remark-katex doesn't work gatsbyjs/gatsby#6648

But the remarkPlugins option works great and is usually the workaround that is eventually used. So exposing this option to the user helps.

Changelog

New

• added a remarkPlugins theme option to be passed to gatsby-plugin-mdx
• added an example on how to use it with the remark-grid-tables remark plugin

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[vpicone]

Awesome! Thanks for this, we don't use remark plugins in our sites so aren't exposed to the issues. Maybe you could add a note for when someone might use one or the other? Even a "if this doesn't work, try this" sort of note.

Just don't want folks to look at gatsbyRemarkPlugins and remarkPlugins and not know which to reach for.

[alaaalii]

Thanks. I added this to the documentation:

The gatsbyRemarkPlugins option is compatible with all gatsby-remark-* plugins, for example gatsby-remark-mermaid. If a gatsby remark plugin does not work, you can try calling the (underlying) remark plugin directly using the remarkPlugins option.

Hopefully this wording is good enough to explain the difference?

[vpicone]

Brilliant fixes, thank you again!

[vpicone]

Brilliant! Love the clarity you brought to that section of the docs.