Add feature metrics for content gap features

The dataframe of articles mapped to content gap features is joined with a set of metrics using article_id. The set of metrics is:

• Article quality score (article-quality#1 (closed))
• Pageviews (https://wikitech.wikimedia.org/wiki/Analytics/Data_Lake/Traffic/Pageview_hourly)
• Revision Counts (https://wikitech.wikimedia.org/wiki/Analytics/Data_Lake/Edits/MediaWiki_history)

Where possible, this should be done via a hive/sql query, otherwise via a dataframe reading from hdfs/parquet directly

Note that the feature metric dataframes (i.e. before they are joined with the content gap features) are timeseries, there will be multiple values per article (e.g. monthly)