Create GTM review issue template

We have been tracking GTM reviews in GitHub through issues. The template is very similar to the code review template.

.github/ISSUE_TEMPLATE/z_gtm_review.md

@@ -0,0 +1,22 @@
+---
+name: "GTM Review"
+about: Google Tag Manager code review request
+title: '[GTM Review] {{ title of card here }}'
+labels:
+assignees: ''
+---
+
+## One-line summary
+
+Review and publish GTM [workspace name]
+
+## Significant changes and points to review
+
+
+
+## Issue
+
+Issue:
+Supporting bedrock changes:
+
+## Testing