feat: 在查询postgresql表字段时同时获取字段描述信息

[imloama]

修改gdb_driver_pgsql.go，增加从pg_description表获取字段描述信息，方便后续gf-cli时生成代码中缺少pg字段注释的问题。

[codecov-commenter]

Codecov Report

Merging #1280 (b935a8c) into develop (eb723e4) will decrease coverage by 0.05%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop    #1280      +/-   ##
===========================================
- Coverage    69.13%   69.08%   -0.06%     
===========================================
  Files          375      375              
  Lines        26611    26612       +1     
===========================================
- Hits         18398    18385      -13     
- Misses        6670     6683      +13     
- Partials      1543     1544       +1     

Impacted Files	Coverage Δ
database/gdb/gdb_driver_pgsql.go	0.00% <0.00%> (ø)
net/gtcp/gtcp_pool.go	28.78% <0.00%> (-10.61%)	⬇️
os/gspath/gspath_cache.go	83.78% <0.00%> (-8.11%)	⬇️
net/gtcp/gtcp_conn.go	30.53% <0.00%> (-2.30%)	⬇️

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