Write glossary/taxonomy for push archival process and mechanism

SWH provides different channels to push software artifacts into the archive, which are used or will be used for software archival. This push process of software artifacts isn't documented and should be with a first draft of a glossary. The items that should be defined:

save code now
software curation
deposit
sparse deposit
metadata deposit
moderation vs curation
original artifact [?]
metadata encapsulation [?]

Migrated from T1839 (view on Phabricator)