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/triggers.go

@@ -2,8 +2,39 @@ package proxy
 
 import (
 	"fmt"
+
+	"github.com/dokku/dokku/plugins/common"
 )
 
+// TriggerInstall runs the install step for the proxy plugin
+func TriggerInstall() error {
+	if err := common.PropertySetup("proxy"); err != nil {
+		return fmt.Errorf("Unable to install the proxy plugin: %s", err.Error())
+	}
+
+	if err := common.MigrateConfigToProperties("proxy", []common.MigrateConfigEntry{
+		{
+			ConfigVar:       "DOKKU_APP_PROXY_TYPE",
+			GlobalConfigVar: "DOKKU_PROXY_TYPE",
+			Property:        "type",
+		},
+		{
+			ConfigVar: "DOKKU_DISABLE_PROXY",
+			Property:  "disabled",
+			Transform: func(value string) string {
+				if value != "" {
+					return "true"
+				}
+				return value
+			},
+		},
+	}); err != nil {
+		return err
+	}
+
+	return nil
+}
+
 // TriggerProxyIsEnabled prints true or false depending on whether the proxy is enabled
 func TriggerProxyIsEnabled(appName string) error {
 	if IsAppProxyEnabled(appName) {
@@ -22,3 +53,22 @@ func TriggerProxyType(appName string) error {
 
 	return nil
 }
+
+// TriggerPostAppCloneSetup creates new proxy files
+func TriggerPostAppCloneSetup(oldAppName string, newAppName string) error {
+	return common.PropertyClone("proxy", oldAppName, newAppName)
+}
+
+// TriggerPostAppRenameSetup renames proxy files
+func TriggerPostAppRenameSetup(oldAppName string, newAppName string) error {
+	if err := common.PropertyClone("proxy", oldAppName, newAppName); err != nil {
+		return err
+	}
+
+	return common.PropertyDestroy("proxy", oldAppName)
+}
+
+// TriggerPostDelete destroys the proxy property for a given app container
+func TriggerPostDelete(appName string) error {
+	return common.PropertyDestroy("proxy", appName)
+}