Allow HTML summary to only show failed tests.

The docs state

Summary reports can also be produced when generating baseline images and hash libraries. The summaries will be written to the results directory. When generating a HTML summary, the --mpl-results-always option is automatically applied. Therefore images for passing tests will also be shown.

However, I believe it would be beneficial to extend the option to only show failed tests. Is this already possible or could this be added to the pytest-mpl?