Make CLI Great (optionally add metadata from sidecar and other files)

[yarikoptic]

Chatting with @nx10 and it seems that some magic is not yet exposed through CLI such as

• indexing metadata from sidecar files
• loading metadata from _scans.tsv files

[yarikoptic]

in principle should also absorb metadata from all relevant metadata files, such as participants.tsv on top level (as just applies to all files per participant) and then sub-*/sub-*_sessions.tsv , and also aware of inheritance principles.