Add index to labels for `type` and project_id`
When loading pages that display the number of open issues, the backend runs a query such as:
SELECT "labels"."id" FROM "labels" WHERE "labels"."type" IN ('ProjectLabel') AND "labels"."project_id" = 1000
This results in an entire scan of the labels
table. To optimize performance,
add the appropriate index to the table.
Closes #27676 (closed)