feat(medusa): List (service + controller) product categories #3004 (#3023)

**What:**

Introduces a store endpoint to retrieve a list of product categories

**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-968

.changeset/nine-queens-sparkle.md

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+---
+"@medusajs/medusa": patch
+---
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+feat(medusa): store - added category list endpoint