replay: use tag based statsd probes

instead of puting everything in the metric name.
Note that this will change existing metric names:

• swh_journal_content_replayer_(get|set)_duration_seconds is replaced with swh_content_replayer_duration_seconds,

• swh_journal_content_replayer_bytes_total -> swh_content_replayer_bytes,

• swh_journal_graph_replayer_object_type_total_duration_seconds (sic) -> swh_graph_replayer_duration_seconds,

• swh_journal_graph_replayer_<objtype>_total -> swh_graph_replayer_operations_total

Tags are

• 'request': ('put' | 'get') for the content replayer durations, and
• 'object_type': ('content'|'directory'|'revision'|'snapshot'|'release'| 'origin'|'origin_visit') for graph replayer probes.