[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

testlib/resources.go

@@ -141,16 +141,10 @@ func setupConfig(configDir string) error {
 		return errors.Wrapf(err, "failed to create config directory %s", configDir)
 	}
 
-	defaultJson := path.Join(configDir, "default.json")
-	err = ioutil.WriteFile(defaultJson, []byte(config.ToJson()), 0644)
-	if err != nil {
-		return errors.Wrapf(err, "failed to write config to %s", defaultJson)
-	}
-
 	configJson := path.Join(configDir, "config.json")
-	err = utils.CopyFile(defaultJson, configJson)
+	err = ioutil.WriteFile(configJson, []byte(config.ToJson()), 0644)
 	if err != nil {
-		return errors.Wrapf(err, "failed to copy file %s to %s", defaultJson, configJson)
+		return errors.Wrapf(err, "failed to write config to %s", configJson)
 	}
 
 	return nil