Add helper to generate dropdown text for security dashboard filters

What does this MR do and why?

Adds a helper function to generate the text that gets displayed within the new GlCollapsibleListbox dropdowns on the security dashboards.

See discussion here: #409701 (comment 1378712587)

Screenshots or screen recordings

N/A

How to set up and validate locally

The added function is not used anywhere yet.

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.