Describe how to find the package name for any app to launch it from Collect

Should be added to https://docs.opendatakit.org/launch-apps-from-collect/ as described at https://forum.opendatakit.org/t/launch-a-scanner-app-and-attach-a-pdf-from-collect/19061/3

Also would be good to note that any app can be launched, even if it doesn't actually give back a value.

Start with the launch-apps-from-collect documentation page and the linked forum discussion. Document how to find an app's package name, and note that Collect can launch apps even when they do not return a value; the page should contain both additions clearly.

Written by the indexing model from the issue text.