Migrate instance-level issues dashboard away from select2

What does this MR do and why?

This follows up on !109149 (merged) where we have made the new-issue-dropdown reusable-enough that it can be used at the instance-level issues dashboard. Up until now, it was only used at the group-level.

This completes 2 tasks:

• We are adding the ability to persist and retrieve the selected project to/from the localStorage. This is basically a backport of what was previously implemented in the ProjectSelectComboButton Js component, which is what we're migrating away from here. It appears that, when the new-issue-dropdown was implemented to replace ProjectSelectComboButton at the group-level, the localStorage capability was not migrated. We are thus not touching the group-level's behavior here, localStorage will remain disabled in that area. However, we'd like to keep supporting the localStorage at the instance-level, hence the few changes in new-issue-dropdown.
• The actual migration: we are replacing ProjectSelectComboButton with new-issue-dropdown at the instance-level issues dashboard.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Navigate to the instance-level issues dashboard at http://gdk.test:3000/dashboard/issues.
2. Use the split dropdown in the top-right to create an issue in some project.

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 #374098 (closed)