Second release candidate for Garage v0.8

Changes since v0.8-rc1:

- Shutdown properly on SIGTERM/SIGHUP and on Windows signals (#396)

- Fix time calculations that made Garage panic in extreme scenarios
  (#398, thanks to Zorun for the intensive testing)

- Add Helm chart for running Garage inside of Kubernetes (#331, thanks
  chemicstry and Maximilien)

- Upgraded build toolchain with Rust >= 1.63.0 (#400)

- Admin API and K2V API: return HTTP 204 No Content when appropriate
  (#376, #403, thanks Tobias Krischer for the contribution)

- Add support for talking to Consul through HTTPS (#405)

- Many documentation updates