Release foundations version 5.8.0

[TheJokr]

Breaking

• Bump tikv-jemallocator to 0.7.0 #217: Users who make their own tikv-jemalloc-sys or tikv-jemalloc-ctl calls will need to update their dependency version to 0.7.0 as well. The upstream jemalloc release brings with it a host of performance and robustness improvements, and direct jemalloc interactions are rare, so we decided a semver violation was warranted in this case.

Added

• User Tracing #223: A separate "user tracing" pipeline is available to record traces that are intended for end-user/customer consumption. The traces are batched based on routing metadata to allow an external service to forward them directly to a user's configured destination(s).
• Make stdio logging fail-soft on write errors #231: LoggingSettings::ignore_io_errors can be enabled to make stdout/stderr/file IO errors non-fatal for foundations' logger. This is disabled by default, preserving the existing behavior of panicking in such situations.

Changed

• Split tracing metrics to allow multiple pipelines #230: Tracing consumer queue metrics carry a new label pipeline="" for the system pipeline. This is backwards compatible, as Prometheus treats an empty label the same as an absent one.