Support marking terms in definition lists with the xpack label

[debadair]

The CSS supported this before the changes to make the label a link to the subscriptions page went in, but I'm not sure if it actually ever worked. I thought I'd used it in the past, but a quick search didn't find any instances of it.

This would be nice in cases where we want to add X-Pack related items to existing lists, such as the settings list on https://www.elastic.co/guide/en/elasticsearch/reference/current/index-modules.html. See elastic/elasticsearch#40880

[debadair]

This is technically possible, but the xpack "bug" is clipped when rendered with the current CSS.

[dedemorton]

we can probably close this no?

[gtback]

Closing this since we're not using the X-Pack label anymore.