Adding sub menus to the left side nav

[eengoron]

Hi Apollo Team! I'm currently trying to use this theme to render API Docs, and while I know this isn't currently supported, are there any plans or good ways to render sub-menus for a page on the left side navigation? Here's our usecase:

We have an Activities endpoint that contains: Calls, Emails and SMS

So when a user clicks on Activities, I want them to navigate to the Activities page, but I also want a sub menu to drop down for calls, emails and SMS. Effectively, I want our side navigation to look something like this:

sidebarCategories: {
          "Getting Started": [
            "topics/authentication",
            "topics/search",
            "topics/timezone-offsets",
            "topics/fields",
            "topics/updating-specific-fields",
            "topics/pagination",
            "topics/webhooks",
            "topics/rate-limits",
            "topics/http-response-codes",
            "topics/api-clients"
          ],
          Resources: [
            { "activities": ["calls", "emails", "sms"] }
          ],
          Changelog: ["changelog"]
        }

Is this something that would be possible, or that you may have a good workaround for?

Thanks!