Migrates legacy dropdown for boards_selector

What does this MR do and why?

This MR migrates legacy GlDropdown to GlCollapsibleListbox according to OKR

Resolves #413021 (closed)

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After	Description
group_level_before.mov	group_level_after.mov	group_level
project_level_before.mov	project_level_after.mov	project_level
key_board_before.mov	keyboard_after.mov	keyboards
		No all boards message

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Go to a project or group
2. Select Plan -> Issue boards
3. Boards dropdown in top left corner

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 #413021 (closed)