Add custom metadata to namespace API and CLI docs (#16633)

* add custom_metadata to ns api docs

* update ns CLI docs to add custom-metadata flag

website/content/api-docs/system/namespaces.mdx

@@ -43,6 +43,19 @@ This endpoint creates a namespace at the given path.
 
 - `path` `(string: <required>)` – Specifies the path where the namespace
   will be created.
+- `custom_metadata` `(map<string|string>: nil)` - A map of arbitrary string to string valued user-provided metadata meant
+  to describe the namespace.
+
+### Sample Payload
+
+```json
+{
+  "custom_metadata": {
+    "foo": "abc",
+    "bar": "123"
+  }
+}
+```
 
 ### Sample Request
 
@@ -50,6 +63,43 @@ This endpoint creates a namespace at the given path.
 $ curl \
     --header "X-Vault-Token: ..." \
     --request POST \
+    --data @payload.json \
+    http://127.0.0.1:8200/v1/sys/namespaces/ns1
+```
+
+## Patch Namespace
+
+This endpoint patches an existing namespace at the specified path.
+
+| Method   | Path                    |
+| :------- | :---------------------- |
+| `PATCH`  | `/sys/namespaces/:path` |
+
+### Parameters
+
+- `path` `(string: <required>)` – Specifies the path of the existing namespace.
+- `custom_metadata` `(map<string|string>: nil)` - A map of arbitrary string to string valued user-provided metadata meant
+  to describe the namespace.
+
+### Sample Payload
+
+```json
+{
+  "custom_metadata": {
+    "foo": "abc",
+    "bar": "123"
+  }
+}
+```
+
+### Sample Request
+
+```shell-session
+$ curl \
+    --header "X-Vault-Token: ..." \
+    --header "Content-Type: application/merge-patch+json"
+    --request PATCH \
+    --data @payload.json \
     http://127.0.0.1:8200/v1/sys/namespaces/ns1
 ```
 
@@ -91,7 +141,11 @@ $ curl \
 ```json
 {
   "id": "gsudj",
-  "path": "ns1/"
+  "path": "ns1/",
+  "custom_metadata": {
+    "foo": "abc",
+    "bar": "123"
+  }
 }
 ```
 

website/content/docs/commands/namespace.mdx

@@ -16,12 +16,24 @@ List all namespaces:
 $ vault namespace list
 ```
 
-Create a namespace at the path `ns1/`:
+Create a namespace at the path `ns1/` with no custom metadata:
 
 ```shell-session
 $ vault namespace create ns1/
 ```
 
+Create a namespace at the path `ns1/` with multiple custom metadata keys:
+
+```shell-session
+$ vault namespace create -custom-metadata=foo=abc -custom-metadata=bar=123 ns1/
+```
+
+Patch an existing namespace at the path `ns1/` to add custom metadata key `bar` and remove key `foo`
+
+```shell-session
+$ vault namespace patch -custom-metadata=bar=123 -remove-custom-metadata=foo ns1/
+```
+
 Delete the namespace at path `ns1/`:
 
 ```shell-session