Add scoped search by issue # and project & to the command palette

What does this MR do and why?

Adds the search by issue # and project & to the command palette

How to set up and validate locally

👣 Enabled the feature flag

rails c 
Feature.enable(:command_palette)

👣 Click on the Global Search icon in the new navigation

👣 Search for recent issue - start typing with # or for the project - start with &

In previous MRs we've added some commands - start with > and users scoped search - start with @.

Note that so far we do not have distinct requirements so I've implemented it as I thought would be reasonable. Feel free to add ideas what could be the next commands in the command palette which you'd like to have access to.

My plan is:

👣 Add more scoped searched - epic, MR, project search by !, &

👣 Jump to project file from command palette

👣 some basic commands context-based - e.g. closing the issue on the issue page or promoting it to an epic. Or some ideas from &8912. Something that would be an easy win

This is an experimental functionality and is the subject of future change or complete removal - we'll get the UX input after a couple of basic experimental commands are added

Screenshots or screen recordings

Related to &8912