apmotel compile error with newer version of otel libraries

[kruskall]

Describe the bug

Projects using both apmotel and otel libraries won't be able to update the otel libraries because of a compile error with apmotel.

Example failure:

elastic/apm-server#12924

 Error: ../../../go/pkg/mod/go.elastic.co/apm/module/apmotel/[email protected]/tracer.go:67:19: impossible type assertion: trace.SpanFromContext(ctx).(*span)
	*span does not implement trace.Span (missing method AddLink)
Error: ../../../go/pkg/mod/go.elastic.co/apm/module/apmotel/[email protected]/tracer.go:96:38: cannot use s (variable of type *span) as trace.Span value in argument to trace.ContextWithSpan: *span does not implement trace.Span (missing method AddLink)
Error: ../../../go/pkg/mod/go.elastic.co/apm/module/apmotel/[email protected]/tracer.go:96:42: cannot use s (variable of type *span) as trace.Span value in return statement: *span does not implement trace.Span (missing method AddLink)
Error: ../../../go/pkg/mod/go.elastic.co/apm/module/apmotel/[email protected]/tracer.go:116:36: cannot use s (variable of type *span) as trace.Span value in argument to trace.ContextWithSpan: *span does not implement trace.Span (missing method AddLink)
Error: ../../../go/pkg/mod/go.elastic.co/apm/module/apmotel/[email protected]/tracer.go:116:40: cannot use s (variable of type *span) as trace.Span value in return statement: *span does not implement trace.Span (missing method AddLink)
Error: ../../../go/pkg/mod/go.elastic.co/apm/module/apmotel/[email protected]/wrapper.go:53:36: cannot use &span{…} (value of type *span) as trace.Span value in argument to trace.ContextWithSpan: *span does not implement trace.Span (missing method AddLink)
Error: ../../../go/pkg/mod/go.elastic.co/apm/module/apmotel/[email protected]/wrapper.go:73:36: cannot use &span{…} (value of type *span) as trace.Span value in argument to trace.ContextWithSpan: *span does not implement trace.Span (missing method AddLink) (compile)

To Reproduce
Steps to reproduce the behavior:

1. create a project
2. use apmotel and otel libs 1.21+
3. run any go command (test, build, etc.)
4. See error

Expected behavior
No error

[dmathieu]

We need to add a (noop because we don't handle links) AddLink method to spans.
open-telemetry/opentelemetry-go#5032