NATS Server 2.15 Release

Previous NATS Server releases, like 2.12 in September of last year and 2.14 in April of this year, focused primarily on the addition of new and exciting features: atomic & fast batch publishing, counters, schedules, etc. The reliability of the server has been gradually increasing throughout as well, with better error handling and the squashing of tons of bugs, but it otherwise was mostly work performed in the background. This release largely forgoes new features and instead focuses entirely on reliability and improving operations, including fully reworking how scales, moves, and peer-removes w