switch to log/slog; move fqdn to a static value from the config file

[actualben]

• adopts slog from stlib, therefore closes adopt sirupsen/logrus (or other) #7
• adopts urfave/cli/v2, therefore closes adopt spf13/cobra (or other) #5
• instead of using the host header, we specify the fqdn we intend to serve in the config file