Add comments of error code

[Sophie-Xie]

What type of PR is this?

• bug
• feature
• enhancement

What problem(s) does this PR solve?

@forest-yuxl add comments of error code for doc, and I just added it to the code comments.
https://docs.nebula-graph.io/master/20.appendix/error-code/

Release notes:

Please confirm whether to be reflected in release notes and how to describe:

None

[codecov-commenter]

Codecov Report

Merging #4201 (e2f5a88) into master (4112c7d) will increase coverage by 0.07%.
The diff coverage is 98.81%.

@@            Coverage Diff             @@
##           master    #4201      +/-   ##
==========================================
+ Coverage   84.91%   84.98%   +0.07%     
==========================================
  Files        1321     1323       +2     
  Lines      131235   131269      +34     
==========================================
+ Hits       111434   111560     +126     
+ Misses      19801    19709      -92     

Impacted Files	Coverage Δ
src/graph/planner/match/MatchClausePlanner.h	100.00% <ø> (ø)
src/graph/scheduler/Scheduler.h	100.00% <ø> (ø)
src/graph/validator/MatchValidator.h	100.00% <ø> (ø)
src/graph/planner/match/MatchClausePlanner.cpp	73.80% <85.71%> (-22.23%)	⬇️
src/graph/planner/match/SegmentsConnector.cpp	98.63% <95.23%> (-1.37%)	⬇️
src/graph/planner/match/MatchPathPlanner.cpp	98.93% <98.93%> (ø)
src/graph/context/ast/CypherAstContext.h	100.00% <100.00%> (ø)
src/graph/planner/match/ArgumentFinder.cpp	90.47% <100.00%> (ø)
src/graph/planner/match/LabelIndexSeek.cpp	98.10% <100.00%> (-0.04%)	⬇️
src/graph/planner/match/MatchPathPlanner.h	100.00% <100.00%> (ø)
... and 66 more

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