RUMM-2295, RUMM-2296, RUMM-2297: Improvement to the reading batch logic

[0xnm]

What does this PR do?

This changes does the following:

• RUMM-2297: Callback is added to notify if batch is not available. This allows to control the upload scheduling mechanism.
• RUMM-2295: Removed the possibility of stack overflow in UploadWorker by converting recursive batch read to the usage of the queue with tasks.
• RUMM-2296: Removed the bottleneck in UploadWorker: now if some feature has long upload which fails (and hence needs to retried), other features are going to have a chance to perform upload before retry happens.

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 #992 (17cb5c7) into feature/sdkv2 (da2dd64) will decrease coverage by 0.01%.
The diff coverage is 86.49%.

@@                Coverage Diff                @@
##           feature/sdkv2     #992      +/-   ##
=================================================
- Coverage          82.91%   82.90%   -0.01%     
=================================================
  Files                295      296       +1     
  Lines               9823     9841      +18     
  Branches            1600     1603       +3     
=================================================
+ Hits                8144     8158      +14     
  Misses              1195     1195              
- Partials             484      488       +4     

Impacted Files	Coverage Δ
...atadog/android/v2/core/internal/storage/Storage.kt	0.00% <0.00%> (ø)
.../android/core/internal/data/upload/UploadWorker.kt	85.71% <88.89%> (+2.38%)	⬆️
...v2/core/internal/data/upload/DataUploadRunnable.kt	100.00% <100.00%> (ø)
...id/v2/core/internal/storage/ConsentAwareStorage.kt	96.81% <100.00%> (+0.11%)	⬆️
...android/log/internal/logger/TelemetryLogHandler.kt	75.00% <0.00%> (-25.00%)	⬇️
...ain/java/com/datadog/opentracing/PendingTrace.java	58.62% <0.00%> (-1.72%)	⬇️
...rsistence/file/batch/PlainBatchFileReaderWriter.kt	85.29% <0.00%> (-0.98%)	⬇️
...rc/main/java/com/datadog/opentracing/DDTracer.java	56.07% <0.00%> (-0.42%)	⬇️
...android/v2/core/internal/DatadogContextProvider.kt	81.03% <0.00%> (ø)
...id/webview/internal/rum/WebViewRumEventConsumer.kt	86.05% <0.00%> (+9.30%)	⬆️

[mariusc83]

LGTM