Allow modules to alter request span attributes

Thank you for the suggestion, but I think it's better to provide an Event than a Hook, cuz hooks are already considered as legacy approach.
I will prepare a separate MR with this.

I reworked the MR https://git.drupalcode.org/issue/opentelemetry-3454318/-/tree/3454318-al... to events, so now you can subscribe to the OpenTelemetrySpanBuilderEvent to alter the whole request span, not even only attributes.
Please check if it works for you.

Also, maybe also add an event for plugins like RequestTrace, ExceptionTrace, etc?

I also added the event dispatching to all plugins, please test.

I want to point out, you dropped the whole API documentation from my initial commit, without any replacement. I'd love to have some information about the Event approach in the README instead, so I will know it is possible at all.

In this approach I see e big flaw ... all properties of the SpanBulder are private ... so I got no clue if I have to rely on an attribute to be present. May be I am missing something, as I am not that deep into the SDK, yet.