refactor discovery

common/go/src/asapo_common/utils/structs.go

discovery/src/asapo_discovery/common/consts.go

discovery/src/asapo_discovery/common/structs.go

...ry/src/asapo_discovery/request_handler/request_handler.go

...asapo_discovery/request_handler/request_handler_consul.go

..._discovery/request_handler/request_handler_consul_test.go

...asapo_discovery/request_handler/request_handler_static.go

..._discovery/request_handler/request_handler_static_test.go

discovery/src/asapo_discovery/server/get_receivers.go

discovery/src/asapo_discovery/server/listroutes.go

discovery/src/asapo_discovery/server/routes_test.go

discovery/src/asapo_discovery/server/server.go

discovery/src/asapo_discovery/server/settings_test.go