fix: failed to parse toml config

[daviderli614]

datanode container CrashLoopBackOff，logs is

ERROR greptime: Fatal error occurs! err.msg=Failed to parse config, source: missing field `metasrv_addrs` for key `meta_client_opts` at line 16 column 1 err.code=InvalidArguments err.source=missing field `metasrv_addrs` for key `meta_client_opts` at line 16 column 1 err.backtrace= 0 <snafu::backtrace_shim::Backtrace as snafu::GenerateImplicitData>::generate::hd7ab405b6b515007

int the https://github.com/GreptimeTeam/greptimedb/blob/develop/config/datanode.example.toml，`metasrv_addr` is update to metasrv_addrs

[daviderli614]

resolve: #73