* feat: frontend instance
* no need to carry column length in `Column` proto
* add more tests
* rebase develop
* create a new variant with already provisioned RecordBatches in Output
* resolve code review comments
* new frontend instance does not connect datanode grpc
* add more tests
* add more tests
* rebase develop
Co-authored-by: luofucong <luofucong@greptime.com>
