* refactor: options and sample configurations
* chore: newline at end of file
* chore: format code
* chore: remove comment and set sample configurations to default values
* chore: use single quoted string in sample configuration files
* refactor: dependency, from frontend depends on datanode to datanode depends on frontend
* wip: start frontend in datanode
* wip: migrate create database to frontend
* wip: impl alter table
* fix: CR comments
* feat: add table id and region ids field to CreateExpr
* chore: rebase develop
* refactor: frontend catalog should set from datanode
* feat: gRPC AddColumn request support add multi columns
* wip: move create table and create-on-insertion to frontend
* wip: error handling
* fix: some unit tests
* fix: all unit tests
* chore: merge develop
* feat: add create/alter-on-insertion to dist_insert/sql_dist_insert
* fix: add region number/catalog/schema to InsertExpr
* feat: add handle_create_table/handle_create_database...
* fix: remove catalog from insert expr
* fix: CR comments
* fix: when running in standalone mode, mysql opts and postgres opts should pass to frontend so that auctually running service can change the port to listen on
* refactor: add a standalone subcommand, move frontend start stuff to cmd package
* chore: optimize create table failure logs
* docs: change readme
* docs: update readme
