[PostgreSQL]Support comments ( index, constraint, trigger )

[k1LoW]

Fix #209 #210

[codecov]

Codecov Report

Merging #220 into master will decrease coverage by 0.84%.
The diff coverage is 92.85%.

@@            Coverage Diff             @@
##           master     #220      +/-   ##
==========================================
- Coverage   68.50%   67.66%   -0.85%     
==========================================
  Files          20       20              
  Lines        3423     3436      +13     
==========================================
- Hits         2345     2325      -20     
- Misses        846      884      +38     
+ Partials      232      227       -5     

Impacted Files	Coverage Δ
drivers/postgres/postgres.go	76.29% <92.85%> (+0.53%)	⬆️
datasource/datasource.go	21.45% <0.00%> (-13.74%)	⬇️

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[k1LoW]

Fix #210