Update `@sentry/node` to v8

[mydea]

We still use v7 of the Node SDK, we should bump our own usage to v8.

We can also explore using ServerRuntimeClient from @sentry/core instead of NodeClient. We only manually create a client, so maybe we can skip the OTEL dependencies etc. here.

[timfish]

I've mostly completed the changes for v8 but the build fails with the previously reported issue with opentelemetry-instrumentation-fetch-node.

I can either wait until this dependency gets removed or drop @sentry/node entirely as a dependency. At this point the only export we need is the Node transport.

[timfish]

Ah, I added that to externals and hit a load of other bundling warnings and issue with otel 😭