Add docker image for gcc 7.2

[justsmth]

Description of changes:

Provides an easy way to create docker image w/ GCC 7.2 for local testing.

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

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.44%. Comparing base (7090b90) to head (ea55960).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1863      +/-   ##
==========================================
- Coverage   78.46%   78.44%   -0.02%     
==========================================
  Files         585      585              
  Lines       99457    99458       +1     
  Branches    14236    14236              
==========================================
- Hits        78038    78023      -15     
- Misses      20784    20799      +15     
- Partials      635      636       +1     

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