RUM-1578: Support returning event metadata to the readers

[0xnm]

What does this PR do?

This is a pre-requisite for the change where we are going to reduce RUM views on the client side.

This PR looks big, but what is does essentially is just shifting the responsibility of the event metadata generation to the feature side (change the signature of writeData to accept newly created class RawBatchEvent(data, meta)), and also makes readData to return this pair of event data +metadata, so that they can be later processed in the upload pipeline.

Signature change of the upload pipeline is similar to what was done in https://github.com/DataDog/dd-sdk-ios/pull/1328/files#diff-a6e4927f6142a31326e45af76631e0538c32b90f419b8856e5d4bad1ecfa99c0.

The structure of RawBatchEvent is similar to https://github.com/DataDog/dd-sdk-ios/pull/1328/files#diff-6e6d2fa1d307e2172f3a6a08142a5f78106dbe374927ba3da5926deb33decbac

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 #1670 (e08208d) into develop (1fc5582) will decrease coverage by 0.11%.
Report is 6 commits behind head on develop.
The diff coverage is 86.36%.

@@             Coverage Diff             @@
##           develop    #1670      +/-   ##
===========================================
- Coverage    83.73%   83.62%   -0.11%     
===========================================
  Files          459      459              
  Lines        15778    15770       -8     
  Branches      2354     2360       +6     
===========================================
- Hits         13211    13187      -24     
- Misses        1938     1946       +8     
- Partials       629      637       +8     

Files	Coverage Δ
...tlin/com/datadog/android/api/net/RequestFactory.kt	100.00% <ø> (ø)
...ain/kotlin/com/datadog/android/core/DatadogCore.kt	84.07% <100.00%> (ø)
...g/android/core/internal/data/upload/DataFlusher.kt	95.00% <100.00%> (+0.26%)	⬆️
...id/core/internal/data/upload/DataOkHttpUploader.kt	94.05% <ø> (+1.19%)	⬆️
.../android/core/internal/data/upload/UploadWorker.kt	86.84% <ø> (ø)
...ndroid/core/internal/data/upload/v2/DataFlusher.kt	100.00% <100.00%> (ø)
...core/internal/data/upload/v2/DataUploadRunnable.kt	96.67% <ø> (ø)
...d/core/internal/data/upload/v2/NoOpDataUploader.kt	50.00% <ø> (ø)
...d/core/internal/persistence/ConsentAwareStorage.kt	98.78% <ø> (ø)
.../core/internal/persistence/NoOpEventBatchWriter.kt	100.00% <ø> (ø)
... and 21 more

... and 15 files with indirect coverage changes