Groups tree enhancements

What does this MR do?

This MR does following enhancements to Groups tree on Group Homepage and Dashboard.

• Updates all the icons to use one from GitLab SVG icons.
• Adds missing updated_at information for Projects shown in Groups tree.
• Adjusts avatar size to be 24x24 pixels.
• Adjusts Group/Project description & last updated information to use color #707070.

Screenshots

Groups Dashboard

Group Homepage

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [ ] Documentation created/updated
• [ ] API support added
• Tests updated for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • [ ] Has been reviewed by Backend
  • [ ] Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• [ ] Internationalization required/considered

What are the relevant issue numbers?

Closes #40533 (closed)