RUM-1822: Use snake case for properties in mapping file event

[0xnm]

What does this PR do?

As requested by the backend team, we will use snake_case for properties in the event form data.

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 #217 (a6d3e56) into develop (f25e114) will increase coverage by 0.15%. The diff coverage is 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #217 +/- ## ============================================= + Coverage 78.05% 78.20% +0.15% - Complexity 186 187 +1 ============================================= Files 22 22 Lines 665 665 Branches 85 85 ============================================= + Hits 519 520 +1 Misses 116 116 + Partials 30 29 -1 ``` | [Files](https://app.codecov.io/gh/DataDog/dd-sdk-android-gradle-plugin/pull/217?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DataDog) | Coverage Δ | | |---|---|---| | [.../datadog/gradle/plugin/internal/DdAppIdentifier.kt](https://app.codecov.io/gh/DataDog/dd-sdk-android-gradle-plugin/pull/217?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DataDog#diff-ZGQtc2RrLWFuZHJvaWQtZ3JhZGxlLXBsdWdpbi9zcmMvbWFpbi9rb3RsaW4vY29tL2RhdGFkb2cvZ3JhZGxlL3BsdWdpbi9pbnRlcm5hbC9EZEFwcElkZW50aWZpZXIua3Q=) | `100.00% <100.00%> (ø)` | | | [...m/datadog/gradle/plugin/internal/OkHttpUploader.kt](https://app.codecov.io/gh/DataDog/dd-sdk-android-gradle-plugin/pull/217?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DataDog#diff-ZGQtc2RrLWFuZHJvaWQtZ3JhZGxlLXBsdWdpbi9zcmMvbWFpbi9rb3RsaW4vY29tL2RhdGFkb2cvZ3JhZGxlL3BsdWdpbi9pbnRlcm5hbC9Pa0h0dHBVcGxvYWRlci5rdA==) | `84.30% <100.00%> (ø)` | | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/DataDog/dd-sdk-android-gradle-plugin/pull/217/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DataDog)