fix(nestjs): Handle multiple OnEvent decorators

[chargome]

Problem is that within the execution there is no way of detecting the triggering event.

• Because of this we now emit a merged transaction name of all applied events – but will add a note on docs that we recommend just putting one decorator per function. We do this by reading the metadata applied on the function by nestjs.
• Adds a flag to avoid double wrapping of the descriptor value (this way we get the correct payload per event and make sure the handler is executed for each event)

closes #15218