Fix "concierge --version" when "go install"ed

Example:

```
$ go install github.com/canonical/concierge@v1.0.2
go: downloading github.com/canonical/concierge v1.0.2
$ concierge --version
concierge version dev (dev)
```

This should say `concierge version v1.0.2`.

It looks like the snap works fine:

```
$ which concierge
/snap/bin/concierge
$ concierge --version
concierge version 1.0.2 (a8143a89a4c2168a153a9260f18f455b966ad490)
```

Start by tracing how the concierge CLI assembles its --version output and how version information is provided when installed with Go. Reproduce the issue with go install github.com/canonical/concierge@v1.0.2, then run concierge --version; done means it reports concierge version v1.0.2 rather than dev.

Written by the indexing model from the issue text.