Allow for filename to be passed to `.to_lalinference` method in the PESummary class

The purpose of this MR is to allow the user to pass a custom filename for the .to_lalinference method in the PESummary class.

This is ready to merge (subject to passing CI).

approved this merge request

enabled an automatic merge when the pipeline for e6d3047f succeeds

merged

mentioned in commit b75d8565