Attempt EZP-22932: Add commit type configuration to Solr handler

Doc is not really clear if it is possible to pass all these params on all rest end points, it mostly only documents the format in xml body.

Unsure if we want to expose all in interface, might be it should only allow enable disable via setter, and type via ctor (so injected from config). This would be cleaner to not hardcode 'soft' in the code.