Tsdb/index sampling endpoint

[owen-d]

Wires up a new endpoint (``/loki/api/v1/index/stats) for querying the index with ([]matcher, from, through)`:

$ curl -s localhost:3100/loki/api/v1/index/stats?query=%7Bfilename%3D~%22.%2B%22%7D | jq '.'
{
  "streams": 2,
  "chunks": 17,
  "bytes": 0, # guessing this is zero b/c none of my test data rounded up to a KB for inclusion here
  "entries": 794
}

ref #5428

[grafanabot]

./tools/diff_coverage.sh ../loki-main/test_results.txt test_results.txt ingester,distributor,querier,querier/queryrange,iter,storage,chunkenc,logql,loki

Change in test coverage per package. Green indicates 0 or positive change, red indicates that test coverage for a package fell.

+           ingester	0%
+        distributor	0%
-            querier	-2.9%
+ querier/queryrange	0%
+               iter	0%
+            storage	0%
+           chunkenc	0%
+              logql	0%
+               loki	0%

[DylanGuedes]

lgtm! just a question

[grafanabot]

./tools/diff_coverage.sh ../loki-main/test_results.txt test_results.txt ingester,distributor,querier,querier/queryrange,iter,storage,chunkenc,logql,loki

Change in test coverage per package. Green indicates 0 or positive change, red indicates that test coverage for a package fell.

+           ingester	0%
+        distributor	0%
-            querier	-2.9%
- querier/queryrange	-0.1%
+               iter	0%
+            storage	0%
+           chunkenc	0%
+              logql	0%
+               loki	0%

[slim-bean]

LGTM very exciting