prepare v0.16.0

[bgentry]

Added

• NeverSchedule returns a PeriodicSchedule that never runs. This can be used to effectively disable the reindexer or any other maintenance service. PR #718.
• Add SkipUnknownJobCheck client config option to skip job arg worker validation. PR #731.

Changed

• The reindexer maintenance process has been enabled. As of now, it will reindex only the river_job_args_index and river_jobs_metadata_index GIN indexes, which are more prone to bloat than b-tree indexes. By default it runs daily at midnight UTC, but can be customized on the river.Config type via ReindexerSchedule. Most installations will benefit from this process, but it can be disabled altogether using NeverSchedule. PR #718.

• Periodic jobs now have a "periodic": true attribute set in their metadata to make them more easily distinguishable from other types of jobs. PR #728.

• Snoozing a job now causes its attempt to be decremented, whereas previously the max_attempts would be incremented. In either case, this avoids allowing a snooze to exhaust a job's retries; however the new behavior also avoids potential issues with wrapping the max_attempts value, and makes it simpler to implement a RetryPolicy based on either attempt or max_attempts. The number of snoozes is also tracked in the job's metadata as snoozes for debugging purposes.

  The implementation of the builtin RetryPolicy implementations is not changed, so this change should not cause any user-facing breakage unless you're relying on attempt - len(errors) for some reason. PR #730.

• ByPeriod uniqueness is now based off a job's ScheduledAt instead of the current time if it has a value. PR #734.

[skip ci]

[brandur]