fix: run addindex failed

[dl239]

CREATE INDEX will launch an async task. another CREATE INDEX cmd with the same table fails if the previous task did not complete
close #3399

[codecov]

Codecov Report

Patch coverage: 48.14% and project coverage change: +38.44% 🎉

Comparison is base (d5647d1) 37.25% compared to head (f914298) 75.69%.
Report is 13 commits behind head on main.

Additional details and impacted files

@@              Coverage Diff              @@
##               main    #3393       +/-   ##
=============================================
+ Coverage     37.25%   75.69%   +38.44%     
  Complexity      414      414               
=============================================
  Files           177      701      +524     
  Lines         10294   126722   +116428     
  Branches       1206     1206               
=============================================
+ Hits           3835    95927    +92092     
- Misses         6218    30554    +24336     
  Partials        241      241               

Files Changed	Coverage Δ
src/base/status.h	100.00% <ø> (ø)
src/nameserver/name_server_impl.h	100.00% <ø> (ø)
src/sdk/sql_cluster_router.cc	60.97% <33.33%> (ø)
src/nameserver/name_server_impl.cc	44.85% <37.14%> (ø)
src/schema/index_util.cc	77.47% <75.00%> (ø)

... and 522 files with indirect coverage changes

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[lumianph]

add a message to tell the user that it is an async task