=tes #15165 MetricsKit should not nullpointer on racy graphite usage
The report() call can come from multiple threads in our code,
yet it was opening/closing a shared graphite client instance in this
method, causing NPE when periodic reporting kicked in during a manual
report() call. We want to be able to do this - thus rewrite to safe impl

Removed metrics-graphite dependency, replaced by in house impl.
The previous was using discrete write() calls, which could be entangled
when called from multiple threads, and produce invalid metric lines.
Current impl is simpler and threadsafe, as the lock for write(String) to
aquired for the entire string lenght's write (unlike multiple write calls).

Resolves #15165
Merge pull request #15228 from ktoso/fix-metrics-kit-graphite-client-NPE

=tes #15165 MetricsKit should not nullpointer on racy graphite usage