Feat: Add Docker support

[mako-max]

With this PR Howitzer will generate several files related with Docker/Compose

#317

[codecov]

Codecov Report

Base: 98.85% // Head: 99.02% // Increases project coverage by +0.17% 🎉

Coverage data is based on head (1fbb87b) compared to base (4d64552).
Patch coverage: 99.30% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #321      +/-   ##
==========================================
+ Coverage   98.85%   99.02%   +0.17%     
==========================================
  Files          44       48       +4     
  Lines        1218     1339     +121     
==========================================
+ Hits         1204     1326     +122     
+ Misses         14       13       -1     

Impacted Files	Coverage Δ
generators/root/root_generator.rb	100.00% <ø> (ø)
lib/howitzer/email.rb	100.00% <ø> (ø)
lib/howitzer/web/section_dsl.rb	93.44% <0.00%> (ø)
generators/base_generator.rb	100.00% <100.00%> (ø)
lib/howitzer/capybara_helpers.rb	100.00% <100.00%> (+1.07%)	⬆️
lib/howitzer/mail_adapters/mailgun.rb	100.00% <100.00%> (ø)
lib/howitzer/mail_adapters/mailtrap.rb	100.00% <100.00%> (ø)
lib/howitzer/mail_adapters/onesecmail.rb	100.00% <100.00%> (ø)
lib/howitzer/mail_adapters/testmail.rb	100.00% <100.00%> (ø)
lib/howitzer/mailtrap_api/client.rb	100.00% <100.00%> (ø)
... and 3 more

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