Expose setting CPU SamplingProfiler rate

Background and Motivation

Microsoft-DotNETCore-SampleProfiler currently samples at a fixed rate of 1 ms, defined in ep-sample-profiler.c. In various situations, it would be beneficial to decrease the rate at which the samples are produced, thus lowering the profiling impact on the runtime.

Proposed Feature

Allow configuring the sampling rate in nanoseconds (_sampling_rate_in_ns) as part of the session creation process, preferably before the sampling starts.

Usage Examples

E.g. profiling in production, minimising the performance impact on the runtime.

Previously, this change was also mentioned in these (differently scoped) issues:

• https://github.com/dotnet/runtime/issues/45518
• https://github.com/dotnet/diagnostics/issues/1706#issuecomment-728277744