doc: add apisix_pluginconfig document (#1025)

docs/en/latest/config.json

@@ -38,7 +38,8 @@
         "references/apisix_route_v2beta3",
         "references/apisix_upstream",
         "references/apisix_tls",
-        "references/apisix_cluster_config"
+        "references/apisix_cluster_config",
+        "references/apisix_pluginconfig"
       ]
     },
     {

docs/en/latest/references/apisix_pluginconfig.md

@@ -0,0 +1,33 @@
+---
+title: ApisixPluginConfig/v2beta3 Reference
+---
+
+<!--
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+-->
+
+## Spec
+
+Spec describes the desired state of an ApisixPluginConfig object.
+
+|     Field     |  Type    |                    Description                     |
+|---------------|----------|----------------------------------------------------|
+| plugins         | array    | A series of custom plugins that will be executed once this route rule is matched |
+| plugins[].name | string | The plugin name, see [docs](http://apisix.apache.org/docs/apisix/getting-started) for learning the available plugins. |
+| plugins[].enable | boolean | Whether the plugin is in use |
+| plugins[].config | object | The plugin configuration, fields should be same as in APISIX. |