Create SortingAnalyzer object directly during create_sorting_analyzer

[ecobost]

Three changes (separated in 3 commits):

• Drop support for analyzers without settings.json file. Comment says support will be dropped in "0.102.0/0.103.0" so seems due.
• Check all required input files are present before trying to load a sorting analyzer.
• Create a SortingAnalyzer object directly as the last step of create_binary_folder/create_zarr rather than re-reloading it

Last one might be the more contentious change. I imagine the reloading during the creation was there to make sure everything could be reloaded fine but everything in the folder is already in memory during create_*() so there isn't really a need to save and reload them into memory, it seems more logical to create the SortingAnalyzer right away.

Closes #4410.

[ecobost]

Another change I would propose is to drop saving sorting_provenance.json during SortingAnalyzer.create_binary_folder. create_binary_folder already saves the entire sorting object (including a provenance.json) in sorting/ so no need to save the provenance again with a diff name.
For SortingAnalyzer.create_zarr the provenance still needs to be saved because currently the sorting.zarr objects do not save provenance, we could
a) leave create_zarr untouched (saving sorting as a group and sorting_provenance as a diff group); or
b) save the sorting_provenance as "provenance" subgroup inside the "sorting" group to mimic the structure of the binary_folder analyzer; (and additionally consider modifying BaseSorting.create_zarr so it also saves provenance though that's a diff discussion)