[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/memory_test.go

@@ -26,7 +26,7 @@ func TestMemoryStoreNew(t *testing.T) {
 		require.NoError(t, err)
 		defer ms.Close()
 
-		assert.Equal(t, model.SERVICE_SETTINGS_DEFAULT_SITE_URL, *ms.Get().ServiceSettings.SiteURL)
+		assert.Equal(t, "", *ms.Get().ServiceSettings.SiteURL)
 	})
 
 	t.Run("existing config, initialization required", func(t *testing.T) {
@@ -134,7 +134,7 @@ func TestMemoryStoreSet(t *testing.T) {
 		require.NoError(t, err)
 		assert.Equal(t, oldCfg, retCfg)
 
-		assert.Equal(t, model.SERVICE_SETTINGS_DEFAULT_SITE_URL, *ms.Get().ServiceSettings.SiteURL)
+		assert.Equal(t, "", *ms.Get().ServiceSettings.SiteURL)
 	})
 
 	t.Run("desanitization required", func(t *testing.T) {
@@ -171,7 +171,7 @@ func TestMemoryStoreSet(t *testing.T) {
 			assert.EqualError(t, err, "new configuration is invalid: Config.IsValid: model.config.is_valid.site_url.app_error, ")
 		}
 
-		assert.Equal(t, model.SERVICE_SETTINGS_DEFAULT_SITE_URL, *ms.Get().ServiceSettings.SiteURL)
+		assert.Equal(t, "", *ms.Get().ServiceSettings.SiteURL)
 	})
 
 	t.Run("read-only ignored", func(t *testing.T) {