Adds MR Review instructions focused around Log Field Standardisation

This commit adds Log Field Standard instructions to the gitlab-runner
project. This is intended to help nudge engineers to ensure they are
following the field standardisation in observability practice.

As it stands, this should not block any ongoing engineering efforts,
but it should help to further broadcast the process and pushing
for impact.

Author: Elliot Forbes

.gitlab/duo/mr-review-instructions.yaml

@@ -0,0 +1,24 @@
+---
+# Custom instructions for GitLab Duo Code Review
+# Based on GitLab's official code review guidelines
+
+# References:
+# - Field Standardisation in Observability: https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/observability_field_standardisation/
+
+
+# This file defines custom review criteria that will be applied to specific files
+# during merge request reviews. Instructions are grouped by name and can target
+# multiple file patterns using glob syntax.
+instructions:
+  - name: Log Field Standards
+    fileFilters:
+      - "**/*.go"
+      - "!**/*_test.go"
+    instructions: |
+      Backend engineers should be complying with the new field standardisation in observability best practices
+      1. For any log lines that have been altered:
+        - Ask: "If you are adding or modifying fields that aren't service specific, please ensure that the field is defined within the LabKit Go Fields package"
+        - Remind: "All logging fields should be defined within the LabKit fields package and imported from there provided that they aren't specific to this service Examples are GitLabUserID. Link: https://gitlab.com/gitlab-org/labkit/-/tree/master/fields?ref_type=heads"
+      2. For any new fields being added to log messages:
+        - Check to ensure that these fields are not dynamically generated
+        - Remind: "We're aiming to standardise the fields that we emit across all of our services at GitLab through this approach. Read more about this in https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/observability_field_standardisation/"