Spans representing calls to external services are not being marked as exit spans

[axw]

Describe the bug

https://github.com/elastic/apm/blob/main/specs/agents/tracing-spans.md#exit-spans says

Exit spans are spans that describe a call to an external service, such as an outgoing HTTP request or a call to a database.

We are only setting ExitSpan: true in module/apmredigov8. We should update all other modules that create these kinds of spans.

Note that the spec also says:

A span is considered an exit span if it has explicitly been marked as such; a span's status should not be inferred.

This does not apply to spans created by built-in instrumentation; it applies to custom spans created through the API.

Expected behavior

We should be marking spans representing calls to external services as exit spans.