Break words in sidebar dropdown label items

What does this MR do and why?

Adds gl-break-word-word to label items in the sidebar Labels dropdown to handle edge cases where a label is a single unbroken string, e.g. ~maintenance::database_performance.

Follow up on !102198 (comment 1151489084)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Create a long label with no spaces or hyphens, e.g. ~maintenance::database_performance
2. From an issue, click Edit on labels to open the Labels dropdown
3. Find the long label you created in the list and confirm it wraps

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.