Add a reference to migr8 in the migration docs 🚀

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Co-authored-by: Luca Forstner <luca.forstner@sentry.io>

[Gitflow] Merge master into develop

…EventTargets (#8943)

Update the docs for the current status of the POTEL experiment.

The `ServerRuntimeClient` is a near identical copy of the nextjs
`EdgeClient`. To make it a direct replacement it has constructor options
to override the event `platform`, `runtime`, and `server_name`.

This PR makes yet another copy of the Node `eventbuilder.ts` but after
future PRs to remove the `EdgeClient` and make `NodeClient` extend
`ServerRuntimeClient`, this will be the only copy. I've put the
`eventbuilder` code in utils since some of these functions are used
elsewhere outside of the clients and I don't want to export these from
core and them become part of our public API. This is especially
important since the browser SDK already exports it's own slightly
different `exceptionFromError`.

…8948)

For `Sentry.startSpan()` API, we need to ensure that when the Sentry
Span is finished, we also finish the OTEL Span.

Also adding some tests for these APIs.

In order to align `Span` & `Transaction` for usage in new performance
APIs, this add `name` to the `Span` that also always returns a string.