[SharePoint] Extend Metadata Indexing to custom one about connectors-ruby

[danajuratoni]

@fred-maussion

add context to their documents, Sharepoint Online connector should be able to access and index the custom metada.

Do you have insights what are customers usually defining custom metadata for? Which SharePoint entities(lists, lists items or files) are of interest to have custom metadata?
Specifying which objects are of interest would help a lot, since their ingestion would likely need to be individually handled for SPO.
cc: @artem-shelkovnikov