File-level code coverage reports

[leizor]

This PR changes the code coverage report to output on a per-file level instead of a per-function level. We will also start marking any previous code coverage reports as outdated and minimize them.

[grafanabot]

Go coverage report:

File	%
github.com/grafana/influx2cortex/pkg/errorx/errors.go	67.3%
github.com/grafana/influx2cortex/pkg/errorx/http_translator.go	100.0%
github.com/grafana/influx2cortex/pkg/influx/api.go	95.0%
github.com/grafana/influx2cortex/pkg/influx/errors.go	100.0%
github.com/grafana/influx2cortex/pkg/influx/parser.go	83.8%
github.com/grafana/influx2cortex/pkg/influx/recorder.go	100.0%
github.com/grafana/influx2cortex/pkg/remotewrite/client.go	69.1%
github.com/grafana/influx2cortex/pkg/remotewrite/measured_client.go	88.9%
github.com/grafana/influx2cortex/pkg/remotewrite/recorder.go	100.0%
github.com/grafana/influx2cortex/pkg/tenant/resolver.go	75.6%
github.com/grafana/influx2cortex/pkg/tenant/tenant.go	91.7%
github.com/grafana/influx2cortex/pkg/util/extract_forwarded.go	66.7%
github.com/grafana/influx2cortex/pkg/util/http.go	68.3%
github.com/grafana/influx2cortex/pkg/util/log/experimental.go	0.0%
github.com/grafana/influx2cortex/pkg/util/log/log.go	0.0%
github.com/grafana/influx2cortex/pkg/util/log/rate_limit.go	90.0%
github.com/grafana/influx2cortex/pkg/util/log/wrappers.go	0.0%
github.com/grafana/influx2cortex/pkg/util/push/push.go	60.0%
total	73.1%