create pr-custom-review.yml (#5253)

syntax in accordance to https://github.com/paritytech/pr-custom-review/tree/5814820aa0e5d35412f31dc02f9d130a8b138cae#configuration-syntax

rules in accordance to https://github.com/paritytech/pr-custom-review/blob/da1d81b9fd39705cc8b37f59235283801c818708/rules.md

polkadot/.github/pr-custom-review.yml

+# 🔒 PROTECTED: Changes to locks-review-team should be approved by the current locks-review-team
+locks-review-team: locks-review
+team-leads-team: polkadot-review
+action-review-team: ci
+
+rules:
+  - name: Runtime files
+    check_type: changed_files
+    condition: ^runtime/(kusama|polkadot)/src/[^/]+\.rs$
+    all_distinct:
+      - min_approvals: 1
+        teams:
+          - locks-review
+      - min_approvals: 1
+        teams:
+          - polkadot-review
+
+  - name: Core developers
+    check_type: changed_files
+    condition:
+      include: .*
+      exclude: ^runtime/(kusama|polkadot)/src/[^/]+\.rs$
+    min_approvals: 2
+    teams:
+      - core-devs
+
+prevent_review_request:
+  teams:
+    - core-devs