Specify name on enrich.get_policy as list type (#50217)

This commit updates the enrich.get_policy API to specify name
as a list, in line with other URL parts that accept a comma-separated
list of values. 

In addition, update the get enrich policy API docs
to align the URL part name in the documentation with
the name used in the REST API specs.

Author: russcam

docs/reference/ingest/apis/enrich/get-enrich-policy.asciidoc

@@ -50,7 +50,7 @@ GET /_enrich/policy/my-policy
 [[get-enrich-policy-api-request]]
 ==== {api-request-title}
 
-`GET /_enrich/policy/<enrich-policy>`
+`GET /_enrich/policy/<name>`
 
 `GET /_enrich/policy`
 
@@ -64,7 +64,7 @@ include::put-enrich-policy.asciidoc[tag=enrich-policy-api-prereqs]
 [[get-enrich-policy-api-path-params]]
 ==== {api-path-parms-title}
 
-`<enrich-policy>`::
+`<name>`::
 +
 --
 (Optional, string)

x-pack/plugin/src/test/resources/rest-api-spec/api/enrich.get_policy.json

@@ -11,8 +11,8 @@
           "methods": [ "GET" ],
           "parts": {
             "name": {
-              "type" : "string",
-              "description" : "The name of the enrich policy"
+              "type" : "list",
+              "description" : "A comma-separated list of enrich policy names"
             }
           }
         },