Currently, GCS KV client only has blocking API. Calling them from dashboard event loop can block other operations for many seconds, leading to failures such as taking too long (> 2min) to submit a job and making nightly tests fail (#21699). This PR offloads the blocking work to a separate thread. Implementing async GCS KV API will be done in the future.
This is part of gcs ha project. This PR try to bootstrap dashboard with gcs address instead of redis.
Co-authored-by: mwtian <81660174+mwtian@users.noreply.github.com>