Generalise multiplex triggering behaviour to enable multiplex clustering on additional beamlines

[amyjaynethompson]

Depending on the needs of the beamline, multiplex is either triggered with xia2-dials or after xia2-dials. When it is triggered with xia2-dials, additional checks are done to abort multiplex if subsequent datasets are still processing. This eases the load on the cluster (needed for VMXi which otherwise runs too many jobs). For other beamlines, multiplex is triggered after xia2-dials on each job in a sample group. This is helpful when the beamline uses multiplex for data quality feedback mid-experiment. Previously, the triggering behaviour was determined by the existence of clustering (as only VMXi was using this feature). To generalise to other beam lines, clustering and trigger-method have been separated in this PR. Corresponding recipe updates to be found in zocalo.