create multiple Products

[haofrank]

• add POST api to create multiple Products
• update the api info to README

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (61daf9a) 96.26% compared to head (4bff35e) 96.50%.

❗ Current head 4bff35e differs from pull request most recent head a2e3165. Consider uploading reports for the commit a2e3165 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #46      +/-   ##
==========================================
+ Coverage   96.26%   96.50%   +0.23%     
==========================================
  Files           8        8              
  Lines         321      343      +22     
==========================================
+ Hits          309      331      +22     
  Misses         12       12              

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[ZzSteven-Wang]

One minor fix needed to the docstring. Others look good.