Wishlist for breaking changes

This issue will collect changes we want to do to the dataset export, but cannot without breaking existing consumers. If we ever need to change the format, we will apply these changes at the same time to only disrupt consumers once.

• switch from timestamp to timestamp with timezone for revision and release timestamps; otherwise the Java library (and any spec-compliant user of the C++ library) will shift them: swh-graph#4788 (closed)
• rename committer_offset to committer_date_offset for consistency with swh-storage: !104 (merged)