fix: Remove high cardinality label from duo_workflow_gitlab_response_seconds metric

What does this merge request do and why?

Currently there is a high cardinality endpoint label with the duo_workflow_gitlab_response_seconds prometheus metric.

This fix reduces the cardinality by removing the workflow_id from the endpoint before sending it to prometheus.

endpoint cardinality screenshot

How to set up and validate locally

1. Checkout this branch and run locally with GDK
2. Open local prometheus page (usually http://localhost:8083/) and run a workflow
3. Ensure that the endpoint label for the metric duo_workflow_gitlab_response_seconds does not contain the workflow_id

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.

Relates to #1337 (closed)