feat: scope docker-options to specific procfile processes

Adds a `--process` flag (repeatable) to docker-options:add/remove/clear/list and the new docker-options:list subcommand for querying a single process+phase pair. Process scoping is supported only for the deploy phase since build runs once per app and run covers ad-hoc commands and cron tasks where no Procfile process type is available. Storage moves from `$DOKKU_ROOT/$APP/DOCKER_OPTIONS_*` files to property lists under `/var/lib/dokku/config/docker-options/$APP/{processType}.{phase}`, with `_default_` as the sentinel for app-wide options. The install trigger migrates pre-existing DOCKER_OPTIONS_* files into property lists once and renames them to `.migrated`; a global marker makes re-runs strictly no-op. The legacy docker-args-{build,deploy,run} bash triggers are reimplemented in Go alongside a new docker-args-process-deploy trigger that surfaces per-process options to the scheduler. The :report command exposes one dynamic flag per configured `process.deploy` pair (e.g. `--docker-options-deploy.web`) and supports `--format json`. There is no `--global` flag; omitting `--process` keeps the historical default behaviour, since `--global` elsewhere in dokku means "across all apps". Closes #2441.

docs/development/plugin-triggers.md

@@ -809,7 +809,7 @@ APP="$1"; IMAGE_SOURCE_TYPE="$2"
 
 ### `docker-args-process-deploy`
 
-- Description: `$PROC_TYPE` may be set to magic `_all_` process type to signify global docker deploy options.
+- Description: emits docker arguments scoped to a specific Procfile process type. The `docker-options` plugin implements this trigger to surface options registered via `docker-options:add --process <PROC>`. `$PROC_TYPE` may be empty (or set to the magic `_default_` value) to signify default-scope docker deploy options.
 - Invoked by: `dokku deploy`
 - Arguments: `$APP $IMAGE_SOURCE_TYPE $IMAGE_TAG [$PROC_TYPE $CONTAINER_INDEX]`
 - Example: