[monitoring] Add OpenTelemetry spans in scd/operational_intents_handler

[the-glu]

This is a set of 3 PRs, proposition to add OpenTelemetry to generate optional traces.
You can check the base PR, the one for handlers and the one for datastores.

This PR add as an example spans in pkg/scd/operational_intents_handler.go

Spans look like that:

Idea would be to have that in all handlers.

[mickmis]

Reviewed f99b7de

Do we really want to manually add this tracer to all methods manually? This is quite noisy and error-prone. We cannot have a middleware doing so automatically?

[the-glu]

Following discussions I close that one (that has been partially overwritten by #1391 ).

I do think we want as much inside as possible, but since there is no easy way without having it everywhere, that probably not the correct approach; and if needed we could still add specific span in the future.