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.
Ports the user-facing CLI subcommands and lifecycle triggers from bash to go, mirroring the layout used by the ports plugin. The on-disk format (`DOCKER_OPTIONS_BUILD/DEPLOY/RUN` files), the `docker-args-build/deploy/run` triggers, and every exported helper consumed by other plugins are unchanged. Reserves the `--process` and `--global` flags on add, remove, and clear so usage today exits with a not-yet-implemented error and the surface is locked in ahead of the process-scoping work tracked in #2441.
