Check whether segments are fully loaded while fetching shard leaders (#20991)

[yah01]

Signed-off-by: yah01 yang.cen@zilliz.com

/kind bug
related #20841

see also #20991

[codecov]

Codecov Report

Merging #21139 (49684c8) into 2.2.0 (f209c9c) will increase coverage by 0.04%.
The diff coverage is 81.81%.

@@            Coverage Diff             @@
##            2.2.0   #21139      +/-   ##
==========================================
+ Coverage   82.02%   82.06%   +0.04%     
==========================================
  Files         688      689       +1     
  Lines       93182    93257      +75     
==========================================
+ Hits        76430    76530     +100     
+ Misses      13749    13737      -12     
+ Partials     3003     2990      -13     

Impacted Files	Coverage Δ
internal/querycoordv2/services.go	82.50% <79.31%> (+2.03%)	⬆️
internal/querycoordv2/errors.go	100.00% <100.00%> (ø)
internal/querycoordv2/dist/dist_handler.go	71.71% <0.00%> (-5.93%)	⬇️
internal/querynode/validate.go	75.90% <0.00%> (-1.63%)	⬇️
internal/querynode/impl.go	64.66% <0.00%> (-1.31%)	⬇️
internal/indexcoord/flush_segment_watcher.go	95.90% <0.00%> (-1.23%)	⬇️
internal/distributed/querynode/client/client.go	89.81% <0.00%> (-1.14%)	⬇️
internal/datanode/flow_graph_insert_buffer_node.go	92.43% <0.00%> (-1.13%)	⬇️
internal/querynode/query_node.go	80.61% <0.00%> (-1.03%)	⬇️
internal/mq/msgstream/mq_msgstream.go	78.50% <0.00%> (-1.00%)	⬇️
... and 23 more

[mergify]

@yah01 ut workflow job failed, comment rerun ut can trigger the job again.

[xiaofan-luan]

/lgtm
/approve

[sre-ci-robot]

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