[MM-14400] Programmatically generate default.json (#10551)

* create/update config.json using go generate

* added default config generator
added config-reset to Jenkins and make package, updated defaults to consider 'isNew' flag

* corrections after code review

* fixed Config.isValid to handle empty encryption keys

* fixed Config.isValid to handle empty encryption keys

* fixed Config.isValid to handle empty encryption keys

* isUpdate now only checks for nil

* Addressed review comments, added unit testing for default config generator

* err shadowing

* license

* provide output file for config generator via ENV variable, since go generate doesn't support arguments and we need two output paths (config-reset and package)

* cleanup

* proper defaults for PushNotificationServer and SendPushNotifications

* corrected generating defaults for TrustedProxyIPHeader to be consistent with default.json in master

* Check for empty SiteURL as well as nil

* corrected SiteURL settings and checking

* crazy typos fixed

* corrected tests to newly expected values

* relaxed the checks

* fixed formatting

config/config_generator/generator/generator.go

@@ -0,0 +1,22 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package generator
+
+import (
+	"encoding/json"
+	"os"
+
+	"github.com/mattermost/mattermost-server/model"
+)
+
+func GenerateDefaultConfig(outputFile *os.File) error {
+	defaultCfg := &model.Config{}
+	defaultCfg.SetDefaults()
+	if data, err := json.MarshalIndent(defaultCfg, "", "  "); err != nil {
+		return err
+	} else if _, err := outputFile.Write(data); err != nil {
+		return err
+	}
+	return nil
+}

config/config_generator/main.go

@@ -0,0 +1,34 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/mattermost/mattermost-server/config/config_generator/generator"
+)
+
+func main() {
+	outputFile := os.Getenv("OUTPUT_CONFIG")
+	if outputFile == "" {
+		fmt.Println("Output file name is missing. Please set OUTPUT_CONFIG env variable to absolute path")
+		os.Exit(2)
+	}
+	if _, err := os.Stat(outputFile); !os.IsNotExist(err) {
+		_, _ = fmt.Fprintf(os.Stderr, "File %s already exists. Not overwriting!\n", outputFile)
+		os.Exit(2)
+	}
+
+	if file, err := os.Create(outputFile); err == nil {
+		err = generator.GenerateDefaultConfig(file)
+		_ = file.Close()
+		if err != nil {
+			panic(err)
+		}
+	} else {
+		panic(err)
+	}
+
+}