Add an option to only keep gzipped files when smaller

Sometimes you do not really know whether a file compresses good (enough) with gzip so that it will actually become smaller.

It would be nice to introduce an option which will discard the gzipped file if the resulting file is larger, and just keep the original one.

The issue names no files, tests, or entry points. Start by locating the plugin's gzip processing entry point and existing option handling, then inspect how compressed output is written. Done means an option preserves the original when the gzipped file is larger and keeps the gzipped file when it is smaller, with tests covering both cases.

Written by the indexing model from the issue text.