Use strings as keys to configure server variables

[api-clients-generation-pipeline]

See DataDog/datadog-api-spec#865

[codecov-io]

Codecov Report

Merging #244 (f638588) into master (5c50075) will decrease coverage by 0.20%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #244      +/-   ##
==========================================
- Coverage   35.96%   35.75%   -0.21%     
==========================================
  Files         847      847              
  Lines       72701    73937    +1236     
==========================================
+ Hits        26145    26438     +293     
- Misses      46556    47499     +943     

Impacted Files	Coverage Δ
lib/datadog_api_client/v1/configuration.rb	91.83% <ø> (+0.34%)	⬆️
lib/datadog_api_client/v2/configuration.rb	91.75% <ø> (+0.26%)	⬆️
...2/models/application_key_response_included_item.rb	57.14% <0.00%> (-1.40%)	⬇️
...g_api_client/v2/models/application_key_response.rb	45.26% <0.00%> (-0.98%)	⬇️
...b/datadog_api_client/v2/models/api_key_response.rb	44.21% <0.00%> (-0.96%)	⬇️
...og_api_client/v2/models/partial_application_key.rb	46.53% <0.00%> (-0.95%)	⬇️
...adog_api_client/v2/models/api_key_relationships.rb	42.55% <0.00%> (-0.93%)	⬇️
lib/datadog_api_client/v2/models/full_api_key.rb	45.54% <0.00%> (-0.93%)	⬇️
...ib/datadog_api_client/v2/models/partial_api_key.rb	45.54% <0.00%> (-0.93%)	⬇️
...tadog_api_client/v2/models/full_application_key.rb	45.54% <0.00%> (-0.93%)	⬇️
... and 618 more

---

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[jirikuncar]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 35.75%. Comparing base (5c50075) to head (f638588).
Report is 1922 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #244      +/-   ##
==========================================
- Coverage   35.96%   35.75%   -0.21%     
==========================================
  Files         847      847              
  Lines       72701    73937    +1236     
==========================================
+ Hits        26145    26438     +293     
- Misses      46556    47499     +943     

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