chore(cmd): clean up commands (#9705)

Move infrastructure related commands to under `cmd/infra` and
development stuff to `cmd/dev`. The default build command builds the
regular user facing binaries: syncthing, stdiscosrv, and strelaysrv.

cmd/infra/strelaypoolsrv/README.md

@@ -0,0 +1,24 @@
+# relaypoolsrv
+
+This is the relay pool server for the `syncthing` project, which allows
+community hosted [relaysrv](https://github.com/syncthing/relaysrv)'s to join
+the public pool.
+
+Servers that join the pool are then advertised to users of `syncthing` as
+potential connection points for those who are unable to connect directly due
+to NAT or firewall issues.
+
+There is very little reason why you'd want to run this yourself, as
+`relaypoolsrv` is just used for announcement and lookup of public relay
+servers. If you are looking to setup a private or a public relay, please
+check the documentation for
+[relaysrv](https://github.com/syncthing/relaysrv), which also explains how
+to join the default public pool.
+
+See `relaypoolsrv -help` for configuration options.
+
+##### Third-party attributions
+
+[oschwald/geoip2-golang](https://github.com/oschwald/geoip2-golang), [oschwald/maxminddb-golang](https://github.com/oschwald/maxminddb-golang), Copyright (C) 2015 [Gregory J. Oschwald](mailto:oschwald@gmail.com).
+
+[lib/pq](https://github.com/lib/pq)</a>, Copyright (C) 2011-2013 'pq' Contributors Portions Copyright (C) 2011 Blake Mizerany.