Pajamas migration GlDropdown in source_filter

What does this MR do and why?

This MR migrates legacy GlDropdown to GlCollapsibleListbox according to OKR

Resolves #421248

Screenshots or screen recordings

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Before	After

How to set up and validate locally

1. Go to project
2. Secure -> Policies
3. Source filter on top of the policies list

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.

Related to #421248Pa