Related to #35415
In rolling upgrade, legacy proxy may dispatch load request wit empty
load field list. The upgraded querycoord may report error by mistake
that load field list is changed.
This PR:
- Auto field empty load field list with all user field ids
- Refine the error messag when load field list updates
- Refine load job unit test with service cases
Signed-off-by: Congqi Xia <congqi.xia@zilliz.com>