Add metrics to expconfigfetcher call

Tracks the time to call the expconfigfetcher and whether it updated the
config file or not.

Test:
Ran a build with a "regular" user and verified the metrics indicated
NO_CONFIG and no config file was created.
Ran a build with an "experiment" user and verified the metrics indicated
CONFIG and a googler.json config file was created.

Bug: http://b/227186589
Change-Id: I030e9497c369459ae98c0c4f7765aef6de4c601f