fix(query): Fix histogram query rewrite to exclude summaries

[vishramachandran]

Pull Request checklist

• The commit(s) message(s) follows the contribution guidelines ?
• Tests for the changes have been added (for bug fixes / features) ?
• Docs have been added / updated (for bug fixes / features) ?

Today we ingest summaries are three or more time series. For example, for a summary named foo:

• One or more quantiles can be reported as time series with metric name foo. Today, this is ingested as a gauge in FiloDB.
• We have a sum reported at foo_sum. This is a counter.
• We have a foo_count. This is also a counter.
  Details in the original prom doc

Problem:
When foo_count is queried, we lookup to see if metric name foo exists. If it exists, we simply rewrite the query to foo::count which ends up querying the count column on foo. This is for backward compatibility on prometheus histograms.

In the case of summaries, the count column does not exist on foo and it leads to query failure.

Fix:
Rewrite the query only if the second lookup exists, and additionally has a column called count. This additional check will be true for histograms only.

Testing:
Existing unit tests in MultiSchemaPartitionsExecSpec cover this case.

[sandeep6189]

thanks for taking this up @vishramachandran