Migrate pagination bar dropdown to disclosure

What does this MR do and why?

Migrate pagination bar dropdown to disclosure

Replace generic gl-dropdown usage with disclosure dropdown

Changelog: changed

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Open "New group" (/groups/new#import-group-pane)
2. Use https://gitlab.com as source instance and GeK1Nis4j-SY1X4sqE5c as personal access token (this token is from separate user on GitLab instance with 0 real data available, so we do not expose any security risks here)
3. Ensure pagination is displayed and working

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 #418089 (closed)