Table-friendly footnotes

Callouts only work in code blocks - not in tables,

so in tables we use footnotes.

However the footnote appears, naturally enough, at the foot of the page, which can be a very long way from the table.

e.g. the Asia-Pacific tab at https://docs.couchbase.com/cloud/clouds/cloud-providers.html#supported-regions

or the three footnotes at https://docs.couchbase.com/java-sdk/current/project-docs/compatibility.html#couchbase-feature-availability-matrix

Ideally we'd like them to be immediately after the table - one possible solution may be to allow them to optionally appear within, but at the end of, a block element - or the enclosing `–` of a tab set.