addr in grpc conf

[yesnault]

for now:

GRPC struct {
		Port int `toml:"port" default:"8082"`
} `toml:"grpc"`

want:

GRPC struct {
Addr       string `toml:"addr" default:"" commented:"true" comment:"Listen address without port, example: 127.0.0.1"`
Port int `toml:"port" default:"8082"`
} `toml:"grpc"`

[yesnault]

cc @fredericalix