Rename cat.transform => cat.transforms (#54438)

* Rename cat.transform => cat.transforms

To match the url.

We typically prefer singular url nouns but _cat tends to use plural and
this API does in fact uses `/_cat/transforms`

* also rename the api in the spec and tests

(cherry picked from commit c495d220ac8fedba7f70f82387cd6d6a672b8b14)

x-pack/plugin/src/test/resources/rest-api-spec/api/cat.transforms.json

@@ -1,5 +1,5 @@
 {
-  "cat.transform":{
+  "cat.transforms":{
     "documentation":{
       "url":"https://www.elastic.co/guide/en/elasticsearch/reference/current/cat-transforms.html",
       "description": "Gets configuration and usage information about transforms."

x-pack/plugin/src/test/resources/rest-api-spec/test/transform/transforms_cat_apis.yml

@@ -51,7 +51,7 @@ teardown:
 ---
 "Test cat transform stats hiding headers":
   - do:
-      cat.transform:
+      cat.transforms:
         transform_id: "airline-transform-stats"
   - match:
       $body: |
@@ -61,7 +61,7 @@ teardown:
 ---
 "Test cat transform stats with column selection":
   - do:
-      cat.transform:
+      cat.transforms:
         transform_id: "airline-transform-stats"
         v: true
         h: id,version,source_index,dest_index,search_total,index_total,docp,cdtea,indexed_documents_exp_avg
@@ -90,7 +90,7 @@ teardown:
             "description": "description"
           }
   - do:
-      cat.transform:
+      cat.transforms:
         transform_id: "airline-transform-batch"
         v: true
   - match:
@@ -126,7 +126,7 @@ teardown:
             }
           }
   - do:
-      cat.transform:
+      cat.transforms:
         transform_id: "airline-transform-continuous"
         v: true
   - match: