Support longer archive names for repositories and optimize the process.
Review Request #10372 — Created Jan. 3, 2019 and submitted
Repository names recently got a bump in their max length, but archiving
didn't take advantage of this. They were still capping the repository
name part of the archive name to 50 characters.
This change updates this to introspect the maximum length of repository
names and use this instead of assuming any specific limit. It also
updates the saving to update only the fields that have been modified.
Unit tests passed.