chore: update CODEOWNERS to use teams and add validator workflow (#193)

* chore: update CODEOWNERS to use teams and add validator workflow

- Replace @observIQ/terraform-owners with @observIQ/platformteam
- Add CODEOWNERS validator GitHub Action workflow

PLAT-427

* Update CODEOWNERS validator workflow

- Use actions/checkout@v6
- Use CODEOWNERS_VALIDATOR_TOKEN for org permissions
- Only trigger on pull_request and workflow_dispatch
- Only watch .github/CODEOWNERS path

Author: joe-armstrong

.github/CODEOWNERS

@@ -1 +1 @@
-* @observIQ/terraform-owners
+* @observIQ/platformteam

.github/workflows/codeowners-validator.yml

@@ -0,0 +1,19 @@
+name: Validate CODEOWNERS
+
+on:
+  workflow_dispatch:
+  pull_request:
+    paths:
+      - '.github/CODEOWNERS'
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+
+      - uses: mszostok/codeowners-validator@v0.7.4
+        with:
+          checks: "files,owners,duppatterns,syntax"
+          github_access_token: "${{ secrets.CODEOWNERS_VALIDATOR_TOKEN }}"
+