[FR.] disable sampling flag header can be ignored (configurable)

[yjqg6666]

Which module is your feature request related to?
Profiling

Is your feature request related to a problem?
What are the considerations when the sampling flag was introduced? From the issues and commit history i haven't found any info about it.

If the topo is gatewayApp (10% sampling) --> bizApp1 (100% profiling) --> bizApp2 . The unsampled request through gatewayApp will add pinpoint header "Pinpoint-Sampled: s0". When the bizApp1 receive the request, it will recognize the header and decide not to trace the request, causing the bizApp1 not 100% profiling.

** Solution
We might make the trace header reader ignore the header and treat it as a new trace and make this behavior configurable, default to not ignore the header for BC. It's open to discussion.

PR #8167 has been made.