feat: migrate environment variables to plugin properties

Standardize how environment variables are migrated to properties during
install triggers and migrate all remaining DOKKU_* config vars to their
appropriate plugin properties.

Adds a reusable MigrateConfigToProperties() function in the common
package with Transform callback and ListProperty support, plus a
migrate-config-to-property subcommand for the prop binary so shell
plugins can use the same code path.

Migrated variables and their new property owners:
- DOKKU_APP_PROXY_TYPE/DOKKU_PROXY_TYPE → proxy type
- DOKKU_DISABLE_PROXY → proxy disabled
- DOKKU_PROXY_PORT → ports proxy-port
- DOKKU_PROXY_SSL_PORT → ports proxy-ssl-port
- DOKKU_APP_RESTORE → ps restore
- DOKKU_SKIP_DEPLOY → ps skip-deploy
- DOKKU_START_CMD → ps start-cmd
- DOKKU_DOCKERFILE_START_CMD → ps dockerfile-start-cmd
- DOKKU_DISABLE_APP_AUTOCREATION → apps disable-autocreation
- DOKKU_APP_SHELL → scheduler shell
- DOKKU_SKIP_CLEANUP → builder skip-cleanup
- DOKKU_CHECKS_DISABLED → checks disabled
- DOKKU_CHECKS_SKIPPED → checks skipped
- DOKKU_CHECKS_WAIT → checks wait
- DOKKU_CHECKS_TIMEOUT → checks timeout
- DOKKU_CHECKS_ATTEMPTS → checks attempts
- DOKKU_DEFAULT_CHECKS_WAIT → checks default-wait
- DOKKU_SKIP_ALL_CHECKS → checks disabled (legacy)
- DOKKU_SKIP_DEFAULT_CHECKS → checks skipped (legacy)

Also refactors existing bespoke migration loops in scheduler, ports, ps,
builder, and nginx-vhosts plugins to use the standardized utility.

Removes DOKKU_PARALLEL_ARGUMENTS from documentation (unused in core).
Deprecates fn-migrate-config-to-property bash function.

closes #1558

plugins/proxy/src/triggers/triggers.go

@@ -18,12 +18,25 @@ func main() {
 
 	var err error
 	switch trigger {
+	case "install":
+		err = proxy.TriggerInstall()
 	case "proxy-is-enabled":
 		appName := flag.Arg(0)
 		err = proxy.TriggerProxyIsEnabled(appName)
 	case "proxy-type":
 		appName := flag.Arg(0)
 		err = proxy.TriggerProxyType(appName)
+	case "post-app-clone-setup":
+		oldAppName := flag.Arg(0)
+		newAppName := flag.Arg(1)
+		err = proxy.TriggerPostAppCloneSetup(oldAppName, newAppName)
+	case "post-app-rename-setup":
+		oldAppName := flag.Arg(0)
+		newAppName := flag.Arg(1)
+		err = proxy.TriggerPostAppRenameSetup(oldAppName, newAppName)
+	case "post-delete":
+		appName := flag.Arg(0)
+		err = proxy.TriggerPostDelete(appName)
 	case "report":
 		appName := flag.Arg(0)
 		err = proxy.ReportSingleApp(appName, "", "")