Add empty state for discussion in sidebar
What does this MR do and why?
Adding empty state for discussion in sidebar as per the new designs.
Designs: #385195[Dsn_Mgmt___Empty.png]
![#385195[Dsn_Mgmt___Empty.png]](https://gitlab.com/gitlab-org/gitlab/-/issues/385195/designs/Dsn_Mgmt___Empty.png){kind=link}
MR acceptance checklist
Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.
Screenshots or screen recordings
| Before | After |
|---|---|
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How to set up and validate locally
Steps to verify:
- Login with any user
- Go to any Group > Projects > Issues
- Create a new
Issue - Go to Issue detail page and upload a design/image
- Click on the design to preview
- Check the sidebar for empty state
Related to #438908 (closed)