storage/badger: Apply limit to results after sorting by created_at + type

[narqo]

Following #99

Needs testing

As a user I expect a search query for ALL profile types to return a mixed set of profiles from the time period, ordered by created_at and type. But it seems that if limit parameter is passed, storage sorts the results by type first and cuts the "tail" of the results. E.g. if we store more cpu profiles in the results than the passed limit, and I requested for ALL profiles, I won't get any heap profiles.

An example query:

/api/0/profiles?service=refresh_worker&type=cpu&labels=dc%3Desh&from=2020-06-01T00%3A00%3A00&to=2020-09-11T06%3A21%3A00&limit=600

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Note, there might be the same issue with storage/s3. storage/clickhouse works as expected.