[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

services/filesstore/s3store.go

@@ -287,7 +287,7 @@ func CheckMandatoryS3Fields(settings *model.FileSettings) *model.AppError {
 
 	// if S3 endpoint is not set call the set defaults to set that
 	if settings.AmazonS3Endpoint == nil || len(*settings.AmazonS3Endpoint) == 0 {
-		settings.SetDefaults()
+		settings.SetDefaults(true)
 	}
 
 	return nil