ObserveWithExemplar support other spancontext types

[mdisibio]

What this PR does:
Was researching that Tempo no longer exported exemplars and identified the root cause: The dskit server instrumentation to export request_duration_seconds histogram and exemplars no longer works for apps using the Otel or other (non-jaeger) SDK, because we are only checking for jaeger.SpanContext. This updates it to also support other, including Otel SpanContext and bridgeSpanContext

Because this repo doesn't have a dependency on otel, some work is needed to get the data without access to the underlying types, and a simple interface conversion doesn't seem to be possible.

Therefore this is Draft so we can decide on the approach. It's possible that were is a better method that doesn't use reflection.

Which issue(s) this PR fixes:

Fixes #

Checklist

• Tests updated
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[colega]

I'm working on something that should solve this in a different way, please hold on here ⌛

[colega]

@mdisibio here's what I'm doing: #681