apmotel: embed new opentelemetry interfaces to span/trace/traceprovider (fixes #1542)

[jacksehr]

From #1542:

There was a breaking change in 1.20.0 which affected custom trace API implementations. As a result, the apmotel and similar modules using otel are currently broken and stuck with older versions.
This prevents projects depending on apmotel from bumping to newer otel versions.

Details: https://github.com/open-telemetry/opentelemetry-go/releases/tag/v1.20.0

This release brings a breaking change for custom trace API implementations. Some interfaces (TracerProvider, Tracer, Span) now embed the go.opentelemetry.io/otel/trace/embedded types. Implementors need to update their implementations based on what they want the default behavior to be.

As in the description of the new embedded package:

Implementers of the OpenTelemetry trace API can embed the relevant type from this package into their implementation directly. Doing so will result in a compilation error for users when the OpenTelemetry trace API is extended (which is something that can happen without a major version bump of the API package).

Embedding these interfaces is the simplest way to eliminate all compilation errors. However, it also means we will introduce compilation errors to users of apmotel if/when OpenTelemetry extends any of the embedded interfaces.

There are other options discussed by them here, but essentially, the alternatives are to panic, or noop, when the interfaces are changed. I'm open to suggestions about why either might be preferred, but have initially just gone with their recommendation.

[kruskall]

Thanks!

[kruskall]

@elasticmachine run elasticsearch-ci/docs

[v1v]

run elasticsearch-ci/docs

[kruskall]

@elasticmachine run elasticsearch-ci/docs