fix: Ensure extra attributes are placed on events

[fuzzybinary]

What does this PR do?

Extra attributes were printed but then ignored by the OkHttpUploader, when they should have been added to the event.

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)

[codecov-commenter]

Codecov Report

Merging #228 (452c63f) into develop (92de134) will decrease coverage by 0.06%. The diff coverage is 66.67%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #228 +/- ## ============================================= - Coverage 81.56% 81.50% -0.06% Complexity 205 205 ============================================= Files 26 26 Lines 797 800 +3 Branches 104 104 ============================================= + Hits 650 652 +2 - Misses 111 112 +1 Partials 36 36 ``` | [Files](https://app.codecov.io/gh/DataDog/dd-sdk-android-gradle-plugin/pull/228?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DataDog) | Coverage Δ | | |---|---|---| | [...m/datadog/gradle/plugin/internal/OkHttpUploader.kt](https://app.codecov.io/gh/DataDog/dd-sdk-android-gradle-plugin/pull/228?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DataDog#diff-ZGQtc2RrLWFuZHJvaWQtZ3JhZGxlLXBsdWdpbi9zcmMvbWFpbi9rb3RsaW4vY29tL2RhdGFkb2cvZ3JhZGxlL3BsdWdpbi9pbnRlcm5hbC9Pa0h0dHBVcGxvYWRlci5rdA==) | `82.54% <66.67%> (-0.39%)` | :arrow_down: |