Update PostgresStorageAdapter.js

[vitaly-t]

• proper use of the connections
• proper integrity: creating tables within a single transaction.

[codecov]

Codecov Report

Merging #4094 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4094      +/-   ##
==========================================
+ Coverage   90.71%   90.72%   +0.01%     
==========================================
  Files         116      116              
  Lines        7916     7918       +2     
==========================================
+ Hits         7181     7184       +3     
+ Misses        735      734       -1

Impacted Files	Coverage Δ
...dapters/Storage/Postgres/PostgresStorageAdapter.js	96.51% <100%> (ø)	⬆️
src/RestWrite.js	93.16% <0%> (+0.18%)	⬆️

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[flovilmart]

Thanks @vitaly-t !