Remove unnecessary Redis calls in issue endpoints

What does this MR do and why?

We only need to track the recent issue view in the #show action. This prevents the Redis calls from being made for the #discussions.json, #can_create_branch, and #related_branches actions.

How to set up and validate locally

1. Open an issue
2. Check the Redis calls in the performance bar for the AJAX requests. There should be no Redis calls with recent_items:* keys.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.