Add min and max quantity query params to list items API

[prr79]

Addresses issue #88

ip:8080/shopcarts/10/items?quantity=3&min_quantity=1&max_quantity=2 - would ignore min and max quantities and just query for items with quantity=3
ip:8080/shopcarts/10/items?min_quantity=1 - query for items with quantity >= 1
ip:8080/shopcarts/10/items?max_quantity=2 - query for items with quantity <= 2
ip:8080/shopcarts/10/items?min_quantity=1&max_quantity=2 - query for items with quantity between 1 and 2.

[codecov]

Codecov Report

Merging #112 (68344bf) into master (bfdf90f) will increase coverage by 0.12%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #112      +/-   ##
==========================================
+ Coverage   97.45%   97.57%   +0.12%     
==========================================
  Files           8        8              
  Lines         393      413      +20     
==========================================
+ Hits          383      403      +20     
  Misses         10       10              

Impacted Files	Coverage Δ
service/routes.py	100.00% <100.00%> (ø)

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[SFARL]

IBM Cloud toolchain: Delivery Pipeline deployed shopcarts to nyu-devops, including commit fe2af75