Add telemetry to when a comment template is used

What does this MR do and why?

For #397070 (closed)

Adds a tracking event for when a user selects a saved comment template in the comment form.

Events & Metrics

User Action	Unique users?	Event Name	Metric Name
Use saved reply	❌	i_code_review_saved_replies_use	counts.i_code_review_saved_replies_use
Use saved reply	✅	i_code_review_saved_replies_use	redis_hll_counters.code_review.i_code_review_saved_replies_use_monthly

Screenshots or screen recordings

N/A; Telemetry

How to set up and validate locally

1. Create a saved comment template for your account (note this is a production link, you should do it in the GDK)
2. Go to an MR where you can leave a comment
3. Select one of your saved comment templates from the toolbar menu item

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.