Upgrade to opawg user-agents-v2

Problem/Motivation

The repo contains a copy of the user-agents.json provided by the Open Podcast Analytics Working Group. This is depracated and will not be supported in the future, see https://github.com/opawg/user-agents

Proposed resolution

Upgrade to user-agents-v2

Remaining tasks

• Remove user-agents.json from repo and replace it with a dependency on the user-agents-v2 github repo
• Adjust queue worker to deal with the new data structure
• Implement support for referers