尝试用 pdctl 更新配置，但失败了，报 "config prefix dashboard not found"
/ # ./pd-ctl config set dashboard/internal-proxy true
Failed to set config: [400] "config item dashboard/internal-proxy not found"
/ # ./pd-ctl config set dashboard.internal-proxy true
Failed to set config: [400] "config prefix dashboard not found"
/ # ./pd-ctl config set dashboard.prefix /dashboard
Failed to set config: [400] "config prefix dashboard not found"
/ # ./pd-ctl config set prefix /dashboard
Failed to set config: [400] "config item prefix not found"
/ # ./pd-ctl config set dashboard.public-path-prefix /dashboard
Failed to set config: [400] "config prefix dashboard not found"
/ # ./pd-ctl config set dashboard.prefix /dashboard
Failed to set config: [400] "config prefix dashboard not found"
/ # ./pd-ctl config set dashboard.internal-proxy true
Failed to set config: [400] "config prefix dashboard not found"