feat: Add support for real tracing

[yeya24]

Now a Tracer interface is added to support adding some fields to the logger https://github.com/argoproj/gitops-engine/blob/master/pkg/utils/tracing/api.go#L10.
We want to add real opentracing/opentelemetry support based on this interface. However, to support real tracing, an additional argument ctx needs to be passed to the StartSpan interface so that the span context can be propagated.

Additionaly, it would be great to refactor this interface. It is hard to add opentracing span options using the current interface.