Mumble server on a Raspberry Pi using Docker

I've recently needed to re-familiarize myself with the basics of Docker after some time away. A quick project to hit the ground running was launching a Mumble server (Murmur) on a Raspberry Pi 4 running Raspbian. There are certainly no shortage of Mumble servers on Docker Hub with the most popular one by far being this one. Unfortunately it won't do us any good as there is no armv7 build. Luckily, since Docker officially supports Alpine for armv7, and Murmur is packaged for Alpine, it is pretty easy to get up and running.