Enhance profiling and allow traces to profiles

[marefr]

What this PR does / why we need it:

Enhances profiling by

• registering godeltaprof endpoints which is more suitable for continuous profiling of memory, goroutines and mutexes
• introducing a new environment variable to enable contention profiling (report of all goroutine blocking and mutex contention events rather than a fraction)
• allowing/enabling use of traces to profiles by labeling spans with profiling attribute (if profiling is enabled).

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:
Planning to document profiling in https://grafana.com/developers/plugin-tools/create-a-plugin/extend-a-plugin/add-logs-metrics-traces-for-backend-plugins or a new page.

[wbrowne]

Just a few nits!