This supplements the release process. We inject Github metadata into two
version.json files; the 'version' value will depend on the type of event,
for release tag events it should be the same as the release tag (i.e. the
app version). This should make version information available to the /config
endpoint on any push, and the frontend should display the backend version.
(For extra safety we will also want to get the frontend version and display
that, but this commit only supplies the barest necessities.)

We add the machinery to get version information and display it discreetly.