Optionally print all config fields and # of uses.
Optionally print all config fields and # of uses.

To run:
`bazel run //config/print:print -- -path=/tmp/testgrid-states/config -print-field-use=true`

GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid,GoogleCloudPlatform/testgrid