posix-gateway: add initial service management API

Implementation of the Service Management API for the posix gateway.
The supported endpoints are `info`, `log/level` and `config`.

GitOrigin-RevId: 58840adc46cf968e92d1e663d9f7ee20894f7a30

Author: kmavromati

go/pkg/dispatcher/api/spec.gen.go

@@ -0,0 +1,25 @@
+load("//lint:go.bzl", "go_library")
+load("@com_github_scionproto_scion//rules_openapi:defs.bzl", "openapi_generate_go")
+
+openapi_generate_go(
+    name = "api_generated",
+    src = "//spec:gateway",
+    client = False,
+)
+
+# exclude the *.gen.go filse in the workspace it's only for editor compatibility.
+# gazelle:exclude *.gen.go
+go_library(
+    name = "go_default_library",
+    srcs = [
+        "api.go",
+        ":api_generated",  # keep
+    ],
+    importpath = "github.com/scionproto/scion/go/pkg/gateway/api",
+    visibility = ["//visibility:public"],
+    deps = [
+        "@com_github_deepmap_oapi_codegen//pkg/runtime:go_default_library",  # keep
+        "@com_github_getkin_kin_openapi//openapi3:go_default_library",  # keep
+        "@com_github_go_chi_chi_v5//:go_default_library",  # keep
+    ],
+)

go/pkg/gateway/api/BUILD.bazel

@@ -0,0 +1,45 @@
+// Copyright 2021 Anapaya Systems
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package api
+
+import (
+	"net/http"
+)
+
+// Server implements the Posix Gateway Service API.
+type Server struct {
+	Config   http.HandlerFunc
+	Info     http.HandlerFunc
+	LogLevel http.HandlerFunc
+}
+
+// GetConfig is an indirection to the http handler.
+func (s *Server) GetConfig(w http.ResponseWriter, r *http.Request) {
+	s.Config(w, r)
+}
+
+// GetInfo is an indirection to the http handler.
+func (s *Server) GetInfo(w http.ResponseWriter, r *http.Request) {
+	s.Info(w, r)
+}
+
+// GetLogLevel is an indirection to the http handler.
+func (s *Server) GetLogLevel(w http.ResponseWriter, r *http.Request) {
+	s.LogLevel(w, r)
+}
+
+// SetLogLevel is an indirection to the http handler.
+func (s *Server) SetLogLevel(w http.ResponseWriter, r *http.Request) {
+	s.LogLevel(w, r)
+}