tsweb: export go_version in standard expvar vars

For monitoring.

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tsweb/tsweb.go

@@ -37,6 +37,7 @@ import (
 func init() {
 	expvar.Publish("process_start_unix_time", expvar.Func(func() any { return timeStart.Unix() }))
 	expvar.Publish("version", expvar.Func(func() any { return version.Long }))
+	expvar.Publish("go_version", expvar.Func(func() any { return runtime.Version() }))
 	expvar.Publish("counter_uptime_sec", expvar.Func(func() any { return int64(Uptime().Seconds()) }))
 	expvar.Publish("gauge_goroutines", expvar.Func(func() any { return runtime.NumGoroutine() }))
 }