Added missing API topics to nav

The following topics were not in the nav so this adds them.

Amy:

• ./api/group_repository_storage_moves.md Amy
• ./api/group_wikis.md Amy
• ./api/merge_request_context_commits.md Amy
• ./api/project_vulnerabilities.md Amy
• ./api/remote_mirrors.md Amy
• ./api/snippet_repository_storage_moves.md Amy

Axil:

• ./api/pages.md Axil
• ./api/protected_environments.md Axil

Evan:

• ./api/visual_review_discussions.md Evan

Marcel:

• ./api/instance_level_ci_variables.md Marcel

Mike:

• ./api/group_import_export.md Mike J
• ./api/resource_access_tokens.md Mike J

Russell:

• ./api/vulnerability_exports.md Russell