feat(oas): pluralize OAS tags (#3315)

## What

Pluralize OAS tags

## Why

OAS tags are commonly used by code generator to group routes under a name space based on a tag. 

Our JS client convention is to use plural, e.g: client.products, client.customers. In order to minimize friction when migrating to a client generated from OAS, tags should be plural as well.

## How

Match tag naming with JS client resource naming.

## Test

* Run `yarn build`
* Run `yarn openapi:generate`
* Run `yarn redocly preview-docs docs/api/admin/openapi.yaml --config=./docs-util/redocly/config.yaml`
* Expect side menu items to be plural.
* Run `yarn redocly preview-docs docs/api/store/openapi.yaml --config=./docs-util/redocly/config.yaml`
* Expect side menu items to be plural.

docs-util/redocly/config.yaml

@@ -138,19 +138,20 @@ decorators:
 
 # Similar config to /www/docs/docusaurus.config.js > redocusaurus
 # Allows to emulate rendering of API public documentation when using `yarn redocly preview-docs openapi.yaml`
-theme.openapi:
-  theme:
-    colors:
-      primary:
-        dart: "#242526"
-    sidebar:
-      width: "250px"
-  disableSearch: true
-  expandResponses: "200,204"
-  generatedPayloadSamplesMaxDepth: 4
-  hideDownloadButton: true
-  hideRequestPayloadSample: true
-  nativeScrollbars: true
-  requiredPropsFirst: true
-  showObjectSchemaExamples: true
-  sortTagsAlphabetically: true
+theme:
+  openapi:
+    theme:
+      colors:
+        primary:
+          dart: "#242526"
+      sidebar:
+        width: "250px"
+    disableSearch: true
+    expandResponses: "200,204"
+    generatedPayloadSamplesMaxDepth: 4
+    hideDownloadButton: true
+    hideRequestPayloadSample: true
+    nativeScrollbars: true
+    requiredPropsFirst: true
+    showObjectSchemaExamples: true
+    sortTagsAlphabetically: true