Cancel queries gracefully

[kmcginnes]

Issue #, if available: #265

Description of changes:

Fixes an issue where cancelling a query is not supported by the database server and the Graph Explorer server will crash.

Other changes:

• Skip logging about "max retries reached" if max retries is 1
• Move error JSON deserialization after log statements in case it fails
• Log out response status and text on failed requests
• Log failed cancellations as warnings

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 12.02%. Comparing base (2a2650e) to head (21b452c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #276   +/-   ##
=======================================
  Coverage   12.02%   12.02%           
=======================================
  Files         410      410           
  Lines       30480    30480           
  Branches      762      762           
=======================================
  Hits         3664     3664           
  Misses      26483    26483           
  Partials      333      333           

Flag	Coverage Δ
unittests	12.02% <ø> (ø)

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[vkagamlyk]

Thanks!