Improvement: extra constructor for DemoMetaData

[TomCools]

Qiute often, the List<DemoDataConfigEntry> config is empty, could be nice to add an extra constructor to not force users to add List.of()).

Triggered by: TimefoldAI/timefold-quickstarts#1192 (comment)

[vikas-prasad-cx]

I'd like to work on this. I'll add a DemoMetaData constructor that omits the config list and defaults it to empty.