Specifying a custom icon in a Bitbucket Connect app doesn't work

Issue Summary

Custom icons for Connect apps don't work. 

Steps to Reproduce

1. Create an app (https://developer.atlassian.com/cloud/bitbucket/getting-started/)
2. Add a repoPage and specify the icon:

"icon": {
    "url": "/icon.png"
}

1. Install the app
2. Navigate to a repository to see the repoPage.

Expected Results

The icon should be the custom icon.

Actual Results

The icon is the default icon.

Workaround

There are a limited number of icons [here|https://docs.atlassian.com/aui/7.9.3/docs/icons.html] that can be specified under "params" for a module. For example: 

"params": {
    "auiIcon": "aui-iconfont-discover"
}

This isn't a perfect workaround, since you still can't set any image for the icon, but it's a bit more customizable than the default icon.