Include information about multi-channel access like `fenix` for `org_mozilla_firefox` and friends

[chutten]

For applications with multiple app ids per channel, we should consider surfacing most prominently the datasets that combine channels in an ergonomic way. At the very least we should mention that they exist.

For example, for Firefox for Android, we don't appear to mention the fenix combination view namespace anywhere, asking people to query specific app ids instead.