Implement refreshing cashed issues count in group sidebar after bulk operations

Summary

Extend Groups::OpenIssuesCountService to include the ability to clear the cached count after a bulk operation has been done. Examples: bulk updating issues state, bulk importing issues.

Related to #243753 (closed)

Tasks

• Clear cached count after bulk updating issues state (closing/reopening) -> !56386 (merged)

Follow-up issue to handle other cases where states can change in large quantities: #329543