Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

internal/cli/health_check.go

@@ -0,0 +1,33 @@
+// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package cli // import "miniflux.app/v2/internal/cli"
+
+import (
+	"net/http"
+	"time"
+
+	"miniflux.app/v2/internal/config"
+	"miniflux.app/v2/internal/logger"
+)
+
+func doHealthCheck(healthCheckEndpoint string) {
+	if healthCheckEndpoint == "auto" {
+		healthCheckEndpoint = "http://" + config.Opts.ListenAddr() + config.Opts.BasePath() + "/healthcheck"
+	}
+
+	logger.Debug(`Executing health check on %s`, healthCheckEndpoint)
+
+	client := &http.Client{Timeout: 3 * time.Second}
+	resp, err := client.Get(healthCheckEndpoint)
+	if err != nil {
+		logger.Fatal(`Health check failure: %v`, err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != 200 {
+		logger.Fatal(`Health check failed with status code %d`, resp.StatusCode)
+	}
+
+	logger.Debug(`Health check is OK`)
+}