Service Desk List - loading state

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	!128981 (merged)
Add loading state and improve empty state	empty states ✅ loading state ⬅ alert for errors with dismiss handle 🚫 handling of next/previous page 🚫 define grid columns if possible at the time (see: !121062 (closed)) 🚫

This MR covers:

• adding a function for defining if the data is being pulled and setting it as a part of the condition for the issuable list

Screenshots or screen recordings

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

Context	Before	After
no issues	before no issues.mov	after no issues.mov
with issues	before with issues.mov	after with issues.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. Visit any other project that has no Service Desk issues as well

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)