Add plugins configuration section to docs (#1727)

Co-authored-by: Michael Gaffney <mgaffney@users.noreply.github.com>

website/content/docs/configuration/index.mdx

@@ -11,6 +11,7 @@ description: Boundary configuration reference.
 [controller]: /docs/configuration/controller
 [worker]: /docs/configuration/worker
 [kms]: /docs/configuration/kms
+[plugins]: /docs/configuration/plugins
 
 Outside of development mode, Boundary controllers and workers are configured using a file.
 The format of this file is [HCL](https://github.com/hashicorp/hcl). In this section you'll find
@@ -39,6 +40,8 @@ After the configuration is written, use the `-config` flag to specify a local pa
 - [`kms`](/docs/configuration/kms): Configures KMS blocks [for various
   purposes](/docs/concepts/security/data-encryption).
 
+- [`plugins`](/docs/configuration/plugins): Configures options for plugins.
+
 - `disable_mlock` `(bool: false)` – Disables the server from executing the
   `mlock` syscall, which prevents memory from being swapped to disk. This is
   fine for local development and testing; in production, it is not recommended

website/content/docs/configuration/plugins.mdx

@@ -0,0 +1,26 @@
+---
+layout: docs
+page_title: Plugins - Configuration
+description: |-
+  The plugins stanza configures plugin-specific parameters.
+---
+
+# `plugin` Stanza
+
+The `plugin` stanza configures plugin-specific parameters. The plugin system was
+introduced in Boundary 0.7.0 and is currently internal; over time, the intent is
+to provide a mechanism for third-party plugins to be able to be used. Available
+plugins are currently bundled with Boundary and executed automatically.
+
+There is currently one configuration parameter available:
+
+```hcl
+plugins {
+  execution_dir = "/var/run/boundary/plugin-exec"
+}
+```
+
+- `execution_dir` - Specifies a directory that Boundary can use to write and
+  execute its built-in plugins. This directory must be writeable by the Boundary
+  user. If not set, Boundary will attempt to create a suitable directory in the
+  system temporary folder.

website/data/docs-nav-data.json

@@ -326,6 +326,10 @@
             "path": "configuration/events/stderr"
           }
         ]
+      },
+      {
+        "title": "plugins",
+        "path": "configuration/plugins"
       }
     ]
   },