[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

Makefile

@@ -535,7 +535,7 @@ config-ldap: ## Configures LDAP.
 config-reset: ## Resets the config/config.json file to the default.
 	@echo Resetting configuration to default
 	rm -f config/config.json
-	cp config/default.json config/config.json
+	OUTPUT_CONFIG=$(PWD)/config/config.json go generate ./config
 
 clean: stop-docker ## Clean up everything except persistant server data.
 	@echo Cleaning