feat(tracing): add userID to lookup traces
feat(tracing): add userID to lookup traces

This commit adds `user_id` as a tag for traces. It helps to lookup and
filter traces we need by userID.

OrgID is harder to get right, so I will open an issue, but it will be
nice to have it in as well.

Signed-off-by: Gianluca Arbezzano <595f0475cb7d517962a097388073aa63576cdfe4@gmail.com>
Co-authored-by: George MacRorie <304d0c1532db14f572c3a321e8f49ce9b29ecf46@influxdata.com>

nooproblem/influxdb,influxdata/influxdb,nooproblem/influxdb,influxdb/influxdb,influxdb/influxdb,nooproblem/influxdb,influxdata/influxdb,nooproblem/influxdb,li-ang/influxdb,influxdb/influxdb,influxdb/influxdb,influxdb/influxdb,li-ang/influxdb,nooproblem/influxdb,influxdb/influxdb