Clarify project-group sharing in docs

Problem to solve

https://gitlab.com/gitlab-com/account-management/emea/scania-ab-group/traton-scania-customer-collaboration-project/-/issues/60#note_1599250923

Further details

Proposal

• Create a conceptual page. Collate information about group sharing and member inheritance to explain how to set up groups for collaborating on projects, applying group sharing, and what to look out for ("best practices").
  • Add a "Best practices" section.
  • Create diagrams to illustrate the explanations.
  • Glossary?
  • Add new page to the left nav.
• Move the explanations and maybe examples from Share a project with a group and Share a group with another group to the new conceptual page.
• Edit Share a group with another group to include only the task, and use UI text instead of the example group names.

Who can address the issue

Technical Writer for grouptenant scale

Other links/references

• https://docs.gitlab.com/ee/user/group/manage.html#share-a-group-with-another-group
• https://docs.gitlab.com/ee/user/project/members/share_project_with_groups.html