Support data segment channel seek to the break point when system start (#5540)

* add DecodeDdOperation

Signed-off-by: yudong.cai <yudong.cai@zilliz.com>

* reload MsgPosition from etcd and seek when system start

Signed-off-by: yudong.cai <yudong.cai@zilliz.com>

* update testcase

Signed-off-by: yudong.cai <yudong.cai@zilliz.com>

* add unittest

Signed-off-by: yudong.cai <yudong.cai@zilliz.com>

* rename const string

Signed-off-by: yudong.cai <yudong.cai@zilliz.com>

* fix unittest

Signed-off-by: yudong.cai <yudong.cai@zilliz.com>

* optimize master unittest

Signed-off-by: yudong.cai <yudong.cai@zilliz.com>

* add msg into dataSegmentChannel to test seek

Signed-off-by: yudong.cai <yudong.cai@zilliz.com>

* fix seek test

Signed-off-by: yudong.cai <yudong.cai@zilliz.com>

* roll back distributed/masterservice/masterservice_test.go

Signed-off-by: yudong.cai <yudong.cai@zilliz.com>