Add option to ignore spans from `browserTracingIntegration`

[mydea]

We used to recommend users to filter spans in beforeSendTransaction. However, this will at some point go away, so this is not really an ideal solution in the future. Instead, the idea is to allow users to filter things in their respective integrations. A good starting point for this, where we do not have this capability yet, is in browserTracingIntegration, which emits a lot of spans.

The concrete solution for this is not 100% defined, but something like a ignoreSpan: (span: Span) => boolean option to browserTracingIntegration may work well. If this returns true, it could emit a non recording span instead of a regular span. This should cover both pageload/navigation spans as well as performance entries etc.