Log when a query is received.

[slim-bean]

Is your feature request related to a problem? Please describe.

There are several places in Loki where we log the outcome of a query, however there are several cases where a query may never finish and no log output is created (one example may be an OOM crash of a querier).

Describe the solution you'd like

Similar to how we do the push request parsed line for writes:

loki/pkg/loghttp/push/push.go

Lines 150 to 162 in 79f0e34

	level.Debug(logger).Log(
	"msg", "push request parsed",
	"path", r.URL.Path,
	"contentType", contentType,
	"contentEncoding", contentEncoding,
	"bodySize", humanize.Bytes(uint64(bodySize.Size())),
	"streams", len(req.Streams),
	"entries", totalEntries,
	"streamLabelsSize", humanize.Bytes(uint64(streamLabelsSize)),
	"entriesSize", humanize.Bytes(uint64(entriesSize)),
	"totalSize", humanize.Bytes(uint64(entriesSize+streamLabelsSize)),
	"mostRecentLagMs", time.Since(mostRecentEntry).Milliseconds(),
	)

I think we should have something similar for queries, as soon as Loki receives the query we should log information about it.

[dannykopping]

We have this partially implemented #7469

We still need this for metadata queries