Tag slow spans, metrics integration

[pavolloffay]

I am just throwing an idea here. Tracing systems usually provide search capability on span duration however users don't know what is a slow duration e.g. 1s 10s, 5ms? We could use metrics integration to tag corresponding slow spans if duration > p999 or something similar. This will require to have a fine grain metric per endpoint and perhaps operation.

cc @pilhuhn

Prerequisite in mp-metrics eclipse/microprofile-metrics#293