Prefer `Gitlab::QueryLimiting.disable!` of `allow(Gitlab::QueryLimiting::Transaction).to receive(:threshold).and_return(X)`

Problem

Using allow(Gitlab::QueryLimiting::Transaction).to receive(:threshold).and_return(X) in specs over Gitlab::QueryLimiting.disable!(issue) in production has the following downsides:

• The threshold is tweaked per spec and not per controller/worker/service
• Follow-up issues are not always linked

See https://docs.gitlab.com/ee/development/database/query_count_limits.html

The only upside of this approach is that a specific threshold is defined instead of disable the query limit completely.

This means that Gitlab::QueryLimiting.disable!(issue) should provide a way of defining a higher, specific threshold. See #468137

Proposed solution

Ban the use of allow(Gitlab::QueryLimiting::Transaction).to receive(:threshold).and_return(X) and suggest to use Gitlab::QueryLimiting.disable!.