Update OpenAPI version and endpoint descriptions (#1243) * Update OpenAPI version and endpoint descriptions Updated version to 1.9.0-rc.4 and improved descriptions for endpoints. * chore: update API docs * Apply suggestion from @lukekim --------- Co-authored-by: Spice Schema Bot <schema-bot@spice.ai> Co-authored-by: Luke Kim <80174+lukekim@users.noreply.github.com>