I'm not sure what Gantt Chart you're trying to embed. Is it some provided by a plugin in JIRA? Which one?
Either way, Confluence has a Gantt macro as you can see here. Though it's not exactly what you asked for, it may be useful.
Jaime Kirch da Silveira
Atlassian Cloud Support
Hi my Community friends! For those who don't know me, I'm a product marketer on the Confluence Cloud team - nice to meet you! For those of you who do, you know that I've been all up in your Co...
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG
You're one step closer to meeting fellow Atlassian users at your local meet up. Learn more about AUGs