feat(medusa): Retrieve (service + controller) a product category (#3004)

What:

Introduces a store endpoint to retrieve a product category

Why:

This is part of a greater goal of allowing products to be added to multiple categories.

How:

- Creates an endpoint in store routes

RESOLVES CORE-967

packages/medusa/src/utils/transformers/tree.ts

@@ -0,0 +1,47 @@
+import { pick } from "lodash"
+import { isDefined } from "medusa-core-utils"
+import { filter, isNull } from "lodash"
+
+// TODO: When we implement custom queries for tree paths in medusa, remove the transformer
+// Adding this here since typeorm tree repo doesn't allow configs to be passed
+// onto its children nodes. As an alternative, we are transforming the data post query.
+export function transformTreeNodesWithConfig(
+  object,
+  config,
+  scope = {},
+  isParentNode = false
+) {
+  const selects = (config.select || []) as string[]
+  const relations = (config.relations || []) as string[]
+  const selectsAndRelations = selects.concat(relations)
+
+  for (const [key, value] of Object.entries(scope)) {
+    const modelValue = object[key]
+
+    if (isDefined(modelValue) && modelValue !== value) {
+      return null
+    }
+  }
+
+  if (object.parent_category) {
+    object.parent_category = transformTreeNodesWithConfig(
+      object.parent_category,
+      config,
+      scope,
+      true
+    )
+  }
+
+  if (!isParentNode && (object.category_children || []).length > 0) {
+    object.category_children = object.category_children.map((child) => {
+      return transformTreeNodesWithConfig(child, config, scope)
+    })
+
+    object.category_children = filter(
+      object.category_children,
+      (el) => !isNull(el)
+    )
+  }
+
+  return pick(object, selectsAndRelations)
+}