Implementation/54749 create add project modal

[akabiru]

https://community.openproject.org/work_packages/54749

🚧 WIP!

• [ ] Overlay autocompleter search results
• [ ] Add leading icon to the show dialog button
  • currently, the show_button slot switches over to an IconButton if any icon is specified Figure out how to add a leading icon.
• [ ] Add include sub-projects checkbox in horizontal form group
• [ ] Define BulkLinkService
  • [ ] Bulk Insertion by default to handle sub-projects and multiple selections
• [ ] Adopt incoming SubHeader Component https://github.com/opf/primer_view_components/pull/116