plugin.config to plugin.yaml migration. (#13070)

* Add plugin.yaml as YAML alternative to plugin.config

Introduce plugin.yaml, a YAML-based configuration file for global
plugins that replaces the legacy line-based plugin.config format.

New capabilities over plugin.config:
- enabled: false to disable plugins without removing them
- load_order for explicit plugin loading priority
- NOTE-level startup log per plugin with load status
- traffic_ctl plugin list via JSONRPC for runtime introspection
- traffic_ctl config convert plugin_config for automated migration
- Fallback: plugin.yaml takes precedence; plugin.config used if absent

* Add inline config field to plugin.yaml

Add the 'config' field to plugin.yaml entries, allowing plugin
configuration to be embedded directly using a YAML block scalar (|).
The literal text is written to a temporary file at startup and passed
to the plugin as an argument. Only scalar values are accepted;
structured YAML is rejected to preserve quoting semantics that
plugins like txn_box rely on.

Author: brbzull0

doc/admin-guide/files/index.en.rst

@@ -31,6 +31,7 @@ Configuration Files
    logging.yaml.en
    parent.config.en
    plugin.config.en
+   plugin.yaml.en
    records.yaml.en
    remap.config.en
    remap.yaml.en
@@ -63,6 +64,10 @@ Configuration Files
    Control runtime loadable plugins available to |TS|, as well as their
    configurations.
 
+:doc:`plugin.yaml.en`
+   YAML-based alternative to :doc:`plugin.config.en` with support for
+   disabling plugins, explicit load ordering, and inline configuration.
+
 :doc:`records.yaml.en`
    Contains many configuration variables affecting |TS| operation.
 

doc/admin-guide/files/plugin.config.en.rst

@@ -23,6 +23,31 @@ plugin.config
 
 .. configfile:: plugin.config
 
+.. warning::
+
+   **Use** :file:`plugin.yaml` **instead.** The :file:`plugin.config` format is
+   maintained for backward compatibility but :file:`plugin.yaml` is the
+   recommended way to configure global plugins. It supports disabling plugins
+   without deleting lines, explicit load ordering, and inline configuration.
+
+   If :file:`plugin.yaml` exists in the configuration directory, |TS| will load
+   plugins from it and ignore :file:`plugin.config` entirely.
+
+   See :doc:`plugin.yaml.en` for the full reference.
+
+   **Migrating:** use ``traffic_ctl`` to convert an existing file automatically:
+
+   .. code-block:: bash
+
+      # Preview the converted output on stdout
+      traffic_ctl config convert plugin_config plugin.config -
+
+      # Write directly to plugin.yaml
+      traffic_ctl config convert plugin_config plugin.config plugin.yaml
+
+   Commented-out lines in :file:`plugin.config` are converted to
+   ``enabled: false`` entries.  Pass ``--skip-disabled`` to drop them instead.
+
 Description
 ===========
 
@@ -71,6 +96,7 @@ Examples
 See Also
 ========
 
+:doc:`plugin.yaml.en`,
 :manpage:`TSAPI(3ts)`,
 :manpage:`TSPluginInit(3ts)`,
 :manpage:`remap.config(5)`