[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

build/release.mk

@@ -34,7 +34,7 @@ package:
 	@# Resource directories
 	mkdir -p $(DIST_PATH)/config
 	cp -L config/README.md $(DIST_PATH)/config
-	cp -L config/config.json $(DIST_PATH)/config
+	OUTPUT_CONFIG=$(PWD)/$(DIST_PATH)/config/config.json go generate ./config
 	cp -RL fonts $(DIST_PATH)
 	cp -RL templates $(DIST_PATH)
 	cp -RL i18n $(DIST_PATH)