Should we have a top level version for libraries?

[ormsbee]

Do we still have a use case for maintaining a library-wide version number? If so, how would we expect it to behave if exporting/importing across instances? Can we remove the top level version for now?

Some background, from my currently-in-progress PR:

# Learning Core doesn't really have a notion of a global version number, but
# we can sort of approximate it by using the primary key of the last publish
# log entry, in the sense that it will be a monotonically increasing
# integer, though there will be large gaps. We use 0 to denote that nothing
# has been done, since that will never be a valid value for a PublishLog pk.
#
# That being said, we should figure out if we really even want to keep a top
# level version indicator for the Library as a whole. In the v1 libs
# implementation, this served as a way to know whether or not there was an
# updated version of content that a course could pull in. But more recently,
# we've decided to do those version references at the level of the
# individual blocks being used, since a Learning Core backed library is
# intended to be used for many LibraryContentBlocks and not 1:1 like v1
# libraries.
version = 0 if last_publish_log is None else last_publish_log.pk

return ContentLibraryMetadata(
    key=library_key,
    title=learning_package.title,
    type=ref.type,
    description=ref.learning_package.description,
    num_blocks=num_blocks,
    version=version,
    last_published=None if last_publish_log is None else last_publish_log.published_at,
    allow_lti=ref.allow_lti,
    allow_public_learning=ref.allow_public_learning,
    allow_public_read=ref.allow_public_read,
    has_unpublished_changes=has_unpublished_changes,
    has_unpublished_deletes=has_unpublished_deletes,
    license=ref.license,
)