Coverage drop comparison by overall coverage

• Adds addition configuration options to facilitate calculating coverage drop by package or overall coverage.
• negative_difference_by: Defines the scope for calculating a drop in code coverage. Possible values are overall and package . Evaluation by package is the default and represents the current behavior. When set to overall, the diff percentage is based on the total code coverage.
• negative_difference_threshold: The percentage drop in coverage that should be allowed, in decimal form (0.05 == 5%). This sets the threshold of allowable variance in the code coverage between builds. The default is 0 (none).
• Configure the number of retention days to apply to uploaded coverage assets.

Thanks to @mlafleur