Support log sampling

[atoulme]

Is your feature request related to a problem? Please describe.
Similar to what is offered with Probabilistic Sampling Processor, offer a log sampler.

Describe the solution you'd like
Ideally, the exact same config as the trace equivalent, with the addition of being able to sample logs according to their severity.

Describe alternatives you've considered
None come to mind.

Additional context
N/A

[pmm-sumo]

I was actually thinking about the same capability recently. One thing I would like to add is sampling across the signals should be hopefully consistent. I think that it's worth considering an option to sample logs with traceid attached separately (so it could be consistent with trace sampling)

[github-actions]

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