SELECT result.configurationitemcapturetime,
         count(result.configurationitemcapturetime) AS NumberOfChanges
FROM 
    (SELECT regexp_replace(configurationItem.configurationItemCaptureTime,
         '(.+)(T.+)', '$1') AS configurationitemcapturetime
    FROM default.awsconfig
    CROSS JOIN UNNEST(configurationitems) AS t(configurationItem)
    WHERE "$path" LIKE '%ConfigHistory%'
            AND configurationItem.configurationItemCaptureTime >= '2018-02-01T%'
            AND configurationItem.configurationItemCaptureTime <= '2018-02-28T%') result
GROUP BY  result.configurationitemcapturetime
ORDER BY  result.configurationitemcapturetime

The results are similar to this:

configurationitemcapturetime    NumberOfChanges
2018-02-02    7
2018-02-03    3
2018-02-07   11
...