Support non-ascii GraphQL headers

[jonathanmos]

What does this PR do?

Support GraphQL headers that are non-ascii by encoding payloads to base64 in the DatadogApolloInterceptor and decoding them in the DatadogInterceptor.

Motivation

What inspired you to submit this pull request?

Additional Notes

Anything else we should know when reviewing?

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)

[datadog-datadog-prod-us1]

🎯 Code Coverage
• Patch Coverage: 93.75%
• Total Coverage: 71.38% (+0.03%)

View detailed report

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 81.25000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.12%. Comparing base (d2a2ec9) to head (a29addc).
⚠️ Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
...n/com/datadog/android/okhttp/DatadogInterceptor.kt	66.67%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3041      +/-   ##
===========================================
- Coverage    71.23%   71.12%   -0.11%     
===========================================
  Files          864      864              
  Lines        31604    31612       +8     
  Branches      5324     5327       +3     
===========================================
- Hits         22510    22482      -28     
- Misses        7582     7606      +24     
- Partials      1512     1524      +12     

Files with missing lines	Coverage Δ
...datadog/android/apollo/DatadogApolloInterceptor.kt	93.55% <100.00%> (+0.22%)	⬆️
...n/com/datadog/android/okhttp/DatadogInterceptor.kt	73.08% <66.67%> (-0.93%)	⬇️

... and 42 files with indirect coverage changes

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[ambushwork]

Well done!