Issues empty state
## What does this MR do?
Adds the empty state for the project, dashboard and group issues.
## Are there points in the code the reviewer needs to double check?
## Why was this MR needed?
## Screenshots (if relevant)
### Filtered to show no issues (on group issues page in this case but also dashboard and projects)
### Project with no issues
### Group with no projects with any issues
## Does this MR meet the acceptance criteria?
- [ ] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
- [ ] Added for this feature/bug
- [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)
## What are the relevant issue numbers?
Closes#20840Closes#20850
See merge request !7309
a7616e03c5