Move to setting version info explicitly in linker flags

We don't have go built-in VCS information in a nix build because the git
repository isn't present. After struggling to build an overlay that
would provide it, I decided this path is easier of just injecting in the
data that we need.

Issue: #5

api/api.go

@@ -322,7 +322,7 @@ type tegolaURLs struct {
 }
 
 func getRoot(ctx context.Context, r *http.Request, q resource.QueryParams) (*about, *nhttp.ErrorWithStatus) {
-	v := version.Get()
+	v := GetVersionInfo()
 	return &about{
 		Environment: config.Environment,
 		SentryDSN:   config.SentryDSNFrontend,