docs: added entity reference (#2047)

* added entity reference

* chore: added github action

* added link to reference

.github/workflows/generate-entity-reference.yml

@@ -0,0 +1,53 @@
+name: Generate Entity Reference
+on: 
+  push:
+    branches:
+      - "master"
+    paths:
+      - packages/medusa/src/models/**
+  pull_request:
+    types:
+      - closed
+    branches:
+      - "master"
+    paths:
+      - packages/medusa/src/models/**
+jobs:
+  services:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Cancel Previous Runs
+        uses: styfle/cancel-workflow-action@0.9.1
+        with:
+          access_token: ${{ github.token }}
+
+      - name: Checkout
+        uses: actions/checkout@v2.3.5
+        with:
+          fetch-depth: 0
+
+      - name: Setup Node.js environment
+        uses: actions/setup-node@v2.4.1
+        with:
+          node-version: "14"
+          cache: "yarn"
+
+      - name: Install dependencies
+        uses: ./.github/actions/cache-deps
+        with:
+          extension: reference
+
+      - name: Build Packages
+        run: yarn build
+
+      - name: Generate Entities Reference
+        run: yarn generate:entities
+
+      - name: Create Pull Request
+        uses: peter-evans/create-pull-request@v4
+        with:
+          commit-message: 'chore(docs): Generated Entities Reference (automated)'
+          base: 'master'
+          title: 'chore(docs): Generated Entities Reference (automated)'
+          labels: 'type: chore'
+          add-paths: docs/content/references/entities/**