Only create supabase db spans when there is a parent span #25806

The supabase integration creates db spans when there is no active span. Each of these spans becomes its own root span and has no context.

Pass onlyIfParent: true to the two startSpanManual calls in packages/core/src/integrations/supabase.ts.

In the browser, queries after the pageload or navigation span ends will then create no span.

Add a test that checks that an operation without an active span creates no span.