suggester statistics

[vladak]

It would be handy to have the elapsed times to rebuild suggester (as logged via changes in #2221) recorded in the configuration (min/max/avg). For this #2229 is needed since the suggester is standalone and therefore cannot import the Statistics class (from web) directly.

[vladak]

The max/count is available as suggester_rebuild_latency* and suggester_init_latency_* meters.