improve the config file

[Nicole00]

• extract some local configs in tag/edge to global config

  • extract some local configs in tag、edge to global config, and reserve the local config which has higher priority.
  • such as type.source, type.sink, batch, partition, header, delimiter, and for database datasource, the user, password, url, driver config can also be extracted to global one.

• add a command to give a simplest config file template according to the datasource

  • spark-submit --master {mode} --class com.vesoft.nebula.exchange.Exchange exchange.jar -generateConfigTemplate csv