Add support for table border

[simurai]

This makes table inside .markdown-body adjust in width based on the content.

Before	After

Note: The border for table is not set and thus the "outer" border is not visible by default. But it can be enabled when using the MediaWiki format in Wikis. See #1127.

Test 👉 https://github.com/simcado/test/wiki/Table-in-MediaWiki-test

---

Fixes #1127

[vercel]

This pull request is being automatically deployed with Vercel (learn more).
To see the status of your deployment, click below or on the icon next to each commit.

🔍 Inspect: https://vercel.com/primer/primer-css/3e9279kad
✅ Preview: https://primer-css-git-table-border.primer.vercel.app

[vdepizzol]

🎉🎉🎉

[koll051]

The width: max-content, unfortunately, breaks tables-in-tables, which are possible in AsciiDoc:

I would much appreciate if this could be solved (or, if this is not the right place to ask, if someone could point me in the right direction). Thank you!