Handle search functionality for Service Desk list

What does this MR do and why?

This is the fourth MR in a series of changes that will change Service Desk issues list from haml file to a Vue app.

Issues	Status
Create the app for service desk issues and add queries that will show all the issues created by the bot and issues count for tabs	✅
Recreate info banner about service desk	✅
Define tokens for search bar	CE search tokens ✅ EE search tokens ✅ searching functionality ⬅
Add sorting functionality	🚫
Add loading state and improve empty state	🚫

This MR covers:

• introduce router to Service Desk Issues list
• handle filtering with tokens

I was originally planning on putting all searching functionality in one MR, but seeing how quickly the diff grew, I decided to split it up even further.

Screenshots or screen recordings

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

Before	After
EE tokens.mov	working search functionality.mov

How to set up and validate locally

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

SERVICE DESK SETUP

1. Setup a service desk on your GDK: https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/howto/service_desk_mail_room.md
2. Send an email to your Service Desk, so you have something to display on the list.

ALTERNATIVE SETUP

1. You can omit Service Desk setup and force an already existing issue to become a SD issue. Open the rails console: rails c
2. Use these commands. Change 7 to the project id that matches the one you want to use for testing:

email = 'your-email@gitlab.com'
project = Project.find 7
issue = project.issues.last
issue.update!(service_desk_reply_to: email, author: User.support_bot)
IssueEmailParticipant.create!(issue: issue, email: email)

1. In rails console enable the feature flag

   Feature.enable(:service_desk_vue_list)
   Feature.enable(:frontend_caching)

2. Visit the project that has Service Desk setup

3. In the main navigation click Monitor, than Service Desk.

4. Click within the search bar and start choosing tokens, click the search icon. The issues list should update and only show matching issues, the tabs count should change and your filters should be reflected in the url of the page.

FYI There is a known problem that Issues in the main navigation highlight when you are on Service Desk view.

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 #413092 (closed)