Log if tracing is enabled/disabled on the Connection as part of the "Slow operation" messages

As seen in recent CBSEs, not all SDK clients enable HELO::Tracing on their mcbp connections - either because they don't enable it by default (e.g. Query prior to MB-64530 / 7.5.0), or because the application has explicitly disabled it.

If Tracing is not enabled then KV-Engine does not generate trace spans for the low-level operation phases if they are not already timed - and as such it can be confusing to try to debug why these "Slow operations" were slow.

For example, without HELO::Tracing enabled then no bg.wait / bg.load spans are reported in the "Slow operation" log message (which would indicate the request had to go to disk to fetch the requested document) - and hence it's ambiguous why an op was slow - was it purely in-memory, or was tracing disabled and hence no spans recorded?

We should add a new element to the message in Cookie::maybeLogSlowCommand which records if tracing was enabled or disabled on the connection to make it more explicit what information was recorded.