**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
* chore: added get route for admin categories API
* chore: add tree method to mock repository
* chore: added changeset to the PR
* chore: rename id to productCategoryId in service
* chore: switch cli option to string
* chore: lint fixes, tests for parent category
* chore: move Nested Categories behind feature flag
* chore: use transformQuery hook in api
* chore: add feature flag in migrations
* chore: remove migration FF, fix FF name
* chore: add free text search + count repo function
* chore: added list endpoint for admin
* chore: added changeset for feature
* chore: address pr review comments
* chore: change oas comment
* chore: add nullable parent category filter + test
**What:**
Introduces a new folder under which repository specs will be placed.
Why:
We don't currently have a good place to test ORM logic or custom queries against the database. The repository folder tests are a place for just exactly that.
How:
Creates an internal package similar to other integration tests - api and plugins.
CORE-965
