Group issues / MRs count in the menu sidebar is slow and can timeout

Summary

Visiting a group with many subgroups/issues/epics (less than 1k as when it's more we cache) may cause a timeout issue when trying to render the Issues/MR count.

Steps to reproduce

1. Have a group with many subgroups
2. Try to open the group
3. Observe error

What is the current bug behavior?

The UI doesn't load due to the query being too expensive

What is the expected correct behavior?

The page loads without issues

Relevant logs and/or screenshots

From BE issue:

• https://log.gprd.gitlab.net/app/r/s/cZ2cJ
• https://console.postgres.ai/gitlab/gitlab-production-main/sessions/32452/commands/100188#visualize-pev2

Output of checks

This bug happens on GitLab.com Enterprise Edition 17.5.0-pre 28210a8a

Possible fixes

Switch how we fetch the count to async GraphQL queries.